Bone oxygenation measurement

ABSTRACT

A bone oximeter probe includes an elongated member and a sensor head at an end of the elongated member to make measurements for a bone. The measurements can indicate the viability or nonviability of the bone. In an implementation, the probe is advanced through an incision in soft tissue, towards the underlying bone, and positioned so that the sensor head faces the bone to be measured. Optical signals are sent from the sensor head and into the bone. The bone reflects some of the optical signals which are then detected so that measurements for the bone can be made. Some of these measurements include an oxygen saturation level value, and a total hemoglobin concentration value of the bone.

BACKGROUND OF THE INVENTION

The human skeletal system provides many different and importantfunctions. The skeletal system gives a body its shape, allows people tostand, gives support for movements such as walking, running, andjumping, and protects the various organs. For example, the vertebralcolumn supports the upright position of the person and protects thespinal cord. The ribs protect the lungs and heart. The pelvis protectsthe intestines.

In addition to support, protection, and movement, bones are alsoresponsible for many physiological processes such as blood cellformation and maintaining blood calcium. Bone marrow, which can be foundin certain types of bone tissue, is responsible for the creation oferythrocytes (i.e., red blood cells), leukocytes (i.e., white bloodcells), and platelets. Certain bone cells are responsible formaintaining normal blood calcium levels. Calcium is used for musclecontraction, metabolism, nerve impulses, and the formation of bloodclots.

Thus, bones play an important role in people's well-being. However,there are few, if any, systems and techniques for objectively measuringthe health of bone. In most cases, the determination of the health of abone is subjective. A physician weighs factors such as the patient'sage, whether or not the patient smokes, medications that the patienttakes, current or past health problems (e.g., cardiovascular disease,asthma, and diabetes), and so forth. After weighing the factors, thephysician develops an opinion of the health of the bone. This opinion isthen used to guide medical decisions or actions. For example, if ahealthy bone is broken, the doctor may recommend one course of action.If an unhealthy bone is broken, the doctor may recommend a differentcourse of action.

However, different physicians may disagree on the health of the bonesince the determination of bone health is subjective. Thus, onephysician may recommend one course of action for a patient and anotherphysician may recommend a different course of action for the samepatient.

Therefore, there is a need for systems and techniques for makingobjective measurements for bone so that medical decisions are moreconsistent with the actual health of the bone.

BRIEF SUMMARY OF THE INVENTION

A bone oximeter probe includes an elongated member and a sensor head atan end of the elongated member to make measurements for a bone. Themeasurements can indicate the viability or nonviability of the bone. Inan implementation, the probe is advanced through an incision in softtissue, towards the underlying bone, and positioned so that the sensorhead faces the bone to be measured. Optical signals are sent from thesensor head and into the bone. The bone reflects some of the opticalsignals which are then detected (e.g., received or collected) so thatmeasurements for the bone can be made. Some of these measurementsinclude an oxygen saturation level value, and a total hemoglobinconcentration value of the bone.

In a specific implementation, a method of making an oxygen saturationmeasurement for a bone includes advancing an elongated probe through anincision in a tissue, where the probe includes a first tube, a sensorhead, connected to the first tube, and first and second fiber opticcables, connected to the sensor head. The ends of the first and secondfiber optic cables are exposed on a surface of the sensor head and anaxis passing through the first tube passes through the surface.

The method further includes positioning the elongated probe in thetissue so the sensor head contacts a bone for which an oxygen saturationparameter is to be measured and causing transmitting of a first lightsignal through the first fiber optic cable to the sensor head. From thesensor head, the first light signal is directed at the bone. Further,after causing transmitting of the first light signal through the firstfiber optic cable, the method includes maintaining a position of theprobe at the bone for the probe to receive a reflection of the firstlight signal from the bone. The reflection of the first light signalfrom the bone is a second light signal. The method also includes causingtransmitting of the second light signal via the second fiber opticcable. The second light signal is transmitted in a direction opposite ofthe transmitting of the first light signal.

The sensor head may include a first source opening, where the firstfiber optic cable is connected to the first source opening, and a firstdetector opening, where the second fiber optic cable is connected to thefirst detector opening. In a specific implementation, a distance betweenthe first source opening and the first detector opening is about 3.5millimeters or less. The surface of the sensor head may have a surfacearea of about 24 square millimeters or less.

The probe may further include a second tube, extending from a proximalend of the first tube to a connector for connecting the probe to aconsole, where the second tube includes a flexible material and thefirst tube includes a rigid material.

In a specific implementation, the method further includes connecting aconnector of the probe to a console including an electronic display,after causing transmitting of the first light signal through the firstfiber optic cable and causing transmitting of the second light signalvia the second fiber optic cable, causing a calculation in the consoleof an oxygen saturation parameter associated with the first light signaland second light signal, and causing displaying of the oxygen saturationparameter on the electronic display. The oxygen saturation parameter mayinclude at least one of an oxygen saturation level value of the bone ora total hemoglobin concentration value of the bone that was measured.

In an implementation, the fiber optic cables extend through a passagewaywithin the probe to the sensor head. The sensor head may include a firstsource structure, a second source structure, a first detector structure,where the first detector structure includes the second fiber opticcable, and a second detector structure. A first distance extends betweenthe first source structure and the first detector structure withouttouching another source or detector structure, a second distance extendsbetween the second source structure and the second detector structurewithout touching another source or detector structure. The firstdistance is different from the second distance.

In another implementation, the sensor head includes a first sourcestructure including the first fiber optic cable, a second sourcestructure, a first detector structure including the second fiber opticcable, and a second detector structure. The first source structure,second source structure, first detector structure, and second detectorstructure are arranged on a line and the axis is perpendicular to theline.

The sensor head may include a first source structure including the firstfiber optic cable, and a first detector structure including the secondfiber optic cable. In a specific implementation, an edge defines thesurface of the sensor head and distances between the first sourcestructure and the edge and between the first detector structure and theedge are about 1.5 millimeters or less.

In a specific implementation, the positioning the elongated probe in thetissue includes positioning the elongated probe in the tissue so thesensor head contacts a first location on the bone. The method furtherincludes after the causing transmitting of the second light signal,reading a first signal quality value on an electronic display of aconsole, repositioning the elongated probe in the tissue so the sensorhead contacts a second location on the bone, different from the firstlocation, and after the repositioning the elongated probe, reading asecond signal quality value on the electronic display of the console.

In a specific implementation, a medical device includes a probe formaking an oxygen saturation measurement for a bone. The probe includes arigid elongated member such as a rigid tube or a solid rod. Theelongated member includes a proximal end, and a distal end, opposite theproximal end. The probe also includes a sensor head, connected to thedistal end of the elongated member, where the sensor head includes firstand second openings, and first and second fiber optic cables. The firstfiber optic cable is connected to the first opening. The second fiberoptic cable is connected to the second opening. The sensor head ispositioned so that light directed into the bone via the first fiberoptic cable travels in a first direction from the proximal end towardsthe distal end and exits the first opening in the first direction. Andlight reflected from the bone enters the second opening in a seconddirection, and travels from the distal end towards the proximal end inthe second direction and through the second fiber optic cable.

The probe further includes a flexible tube, extending from the proximalend of the elongated member, and a connector, connected to the flexibletube.

The medical device may further include a beam combiner, external to theprobe. The beam combiner may include a first input connected to a firstradiation source of a first wavelength and a second input connected to asecond radiation source of a second wavelength, different from the firstwavelength. In an implementation, the first fiber optic cable isconnected to the beam combiner and outputs light of the first wavelengthand light of the second wavelength.

The beam combiner may output light of the first wavelength at a firsttime, and output light of the second wavelength at a second time,different from the first time.

In a specific implementation, a surface of the sensor head including thefirst and second openings is curved concave to complement a convexportion of the bone to be measured. In another implementation, thesurface is curved convex to complement a concave portion of the bone tobe measured.

In a specific implementation, a method for making a bone oximeter probehaving a pad to conform to a surface of a bone to be measured, includesattaching the pad to a block, and creating a set of channels through thepad and block. Each channel extends through the pad and block, from afront surface of the pad to a back surface of the block, opposite thefront surface. The method further includes threading a fiber optic cableinto each channel of the set of channels, positioning the fiber opticcable within each channel so that an end of the fiber optic cable isflush with the front surface of the pad, attaching the fiber optic cableto the channel, and attaching the block to a distal end of a rigid tube.At least a portion of the pad protrudes out from the distal end.

In a specific implementation, the attaching the block to a rigid tubeincludes inserting an opposite end of the fiber optic cable into thedistal end of the rigid tube, advancing the fiber optic cable through apassageway in the rigid tube so that the opposite end of the fiber opticcable exits a proximal end of the rigid tube, opposite the distal end,applying an adhesive to at least one of the block or the passageway, andinserting the block into the distal end of the rigid tube. During theattaching the fiber optic cable to the channel, a portion of the fiberoptic cable may be lying within a passageway of the rigid tube.

In a specific implementation, a bone oximeter probe includes a hollowtube, and a sensor unit. The sensor unit is connected to a distal end ofthe hollow tube. The sensor unit includes a block and a pad, connectedto the block, to conform to surface contours of a bone to be measured.There are first and second channels extending through the block and padto a surface of the pad and first and second fiber optic cables. Thefirst fiber optic cable is connected to the first channel and terminateswithin the first channel before reaching the surface of the pad. Thesecond fiber optic cable is connected to the second channel andterminates within the second channel before reaching the surface of thepad.

The first and second fiber optic cables may extend from a proximal endof the hollow tube, opposite the distal end, and into the pad withoutchanging direction. The pad may include foam. The sensor unit may beinside the hollow tube.

The bone oximeter system can be used to measure StO2, Hgb, or both ofhuman bone. In a specific implementation, the sensor or sensor head ofthe bone oximeter probe is placed on a bone surface, instead of softtissue. StO2 measurements can be made for any bone, including nonhumanbones. Some specific examples of bones for which measurements can bemade include bovine long bone, the spinous process of a pig, the skullof a pig, and the human fibular. The measurements may or may not be usedin spine surgery (e.g., spine fusion surgery). The bone oximeter probetypically has a very small sensor head to accommodate the small surfaceof, for example, the spinous process or transverse process.

In a specific implementation, hypoxic changes in bone are detected andcontinuously monitored with the sensor head when the sensor head is indirect contact with the bone surface. StO2 differences between normaland hypoxic bone may be on the order of about or of at least 15-20percentage points, thus, StO2 is detectable. The differences may be seenin about 20 minutes.

Other objects, features, and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionand the accompanying drawings, in which like reference designationsrepresent like features throughout the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a system for obtaining opticalmeasurements of tissue in a patient.

FIG. 2 shows a more detailed block diagram of a specific implementationof the system of FIG. 1.

FIG. 3 shows a system of the invention including a monitoring consoleand a bone oximeter probe connected to the console.

FIG. 4 shows a block diagram of a system where various parameters ofbone contacted by a sensor probe can be measured and calculated todetermine an indicator of bone health.

FIG. 5 shows a side view of a bone oximeter probe.

FIG. 6 shows a longitudinal cross-sectional view of the tip of the boneoximeter probe shown in FIG. 5 having optical fibers, forming a forwardlooking sensor array.

FIG. 7 shows a front view of a tip of an oximeter probe having a firstsensor arrangement.

FIG. 8 shows a front view of a tip of an oximeter probe having a secondsensor arrangement.

FIG. 9 shows a front view of a tip of an oximeter probe having a thirdsensor arrangement.

FIG. 10 shows a front view of a tip of an oximeter probe having a fourthsensor arrangement.

FIG. 11 shows a front view of a tip of an oximeter probe having a fifthsensor arrangement.

FIG. 12 shows a front view of a tip of an oximeter probe having a sixthsensor arrangement.

FIG. 13 shows a perspective view of a bone oximeter probe with a sensorunit surrounding a tube of the probe.

FIG. 14 shows a perspective view of a bone oximeter probe with a sensorunit which is attached to an outer surface of a tube of the probe.

FIG. 15 shows a side view of a bone oximeter probe with sensor openingson a sidewall of the probe.

FIG. 16 shows a longitudinal cross-sectional view of the tip of theprobe shown in FIG. 15 containing optical fibers, forming a side-lookingsensor array.

FIG. 17 shows a longitudinal cross-sectional view of another probe withboth a forward-looking sensor array and a side-looking sensor array.

FIG. 18 shows a longitudinal cross-sectional view of a tip of a probehaving a deformable sensor head.

FIG. 19 shows a side view of the probe of FIG. 18 being pressed againsta bone.

FIG. 20 shows a longitudinal cross-sectional view of a tip of a probehaving an angled sensor head.

FIG. 21 shows a perspective view of a sensor head that is concave in onedirection.

FIG. 22 shows a perspective view of a sensor head that is concave in twodirections.

FIG. 23 shows a perspective view of a sensor head that is convex in onedirection.

FIG. 24 shows a perspective view of a sensor head that is convex in twodirections.

FIG. 25 shows a block diagram of a bone oximeter system that includes amultiplexer.

FIG. 26 shows a block diagram of a bone oximeter system that includes abeam combiner.

FIG. 27 shows a flowchart of advancing a bone oximeter probe into tissueto obtain bone measurements.

FIG. 28 shows a pictorial diagram of a bone oximeter probe beingadvanced into soft tissue to obtain a measurement of the underlyingbone.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a system 101 for measuring various parameters of a tissuein a patient. The parameters of the tissue measured by the system mayinclude an oxygen saturation level, a total hemoglobin concentration, ablood flow, a pulse, and a signal level of light reflected from thetissue. The system includes a system unit 105 and a sensor probe 108,which is connected to the system unit via a wired connection 112.Connection 112 may be an electrical, optical, or another wiredconnection including any number of wires (e.g., one, two, three, four,five, six, or more wires or optical fibers), or any combination of theseor other types of connections. In other implementations of theinvention, however, connection 112 may be wireless such as via a radiofrequency (RF) or infrared communication.

Typically, the system is used by placing the sensor probe in contact orclose proximity to tissue (e.g., bone or skin or internal organ ortissue) at a site where tissue parameter measurements are desired. Thesystem unit causes an input signal to be emitted by the sensor probeinto the tissue (e.g., human tissue). There may be multiple inputsignals, and these signals may have varying or different wavelengths.The input signal is transmitted into or through the tissue.

Then, after transmission through or reflection off the tissue, thesignal is received at the sensor probe. This received signal is receivedand analyzed by the system unit. Based on the received signal, thesystem unit determines various parameters of the tissue—an oxygensaturation level, a total hemoglobin concentration, a blood flow, apulse, a signal level of light reflected from the tissue. One or anycombinations of these parameters can be displayed on a display screen ofthe system unit.

In an implementation, the system is a tissue oximeter, which can measureoxygen saturation and hemoglobin concentration, without requiring apulse or heart beat. A tissue oximeter of the invention is applicable tomany areas of medicine and surgery including plastic surgery and spinalsurgery. The tissue oximeter can make oxygen saturation and hemoglobinconcentration measurements of tissue where there is no pulse; suchtissue, for example, may have been separated from the body (e.g., aflap) and will be transplanted to another place in the body.

Aspects of the invention are also applicable to a pulse oximeter. Incontrast to a tissue oximeter, a pulse oximeter bases measurements on apulse. A pulse oximeter typically measures the absorbance of light dueto the pulsing arterial blood.

There are various implementations of systems and techniques formeasuring oxygen saturation such as discussed in U.S. Pat. Nos.6,516,209, 6,587,703, 6,597,931, 6,735,458, 6,801,648, and 7,247,142.These patents are assigned to the same assignee as this patentapplication and are incorporated by reference along with all otherreferences cited in this application.

In an implementation, the system is a laser Doppler flow meter, whichcan measure a blood flow, a pulse rate, or both in the tissue. Inprinciple, this technique involves directing a laser beam (e.g., throughoptical fibers) onto a part of the tissue and receiving, with the aid ofan appropriate detector, part of the light scattered and reflected backby that part of the tissue that is irradiated by the laser beam. Whenlight hits moving blood cells, the light undergoes a change inwavelength, which may be referred to as a Doppler shift, while lighthitting nonmoving tissue is unchanged. The magnitude and frequencydistribution of these changes in wavelength are directly related to thenumber and velocity of blood cells but unrelated to their direction ofmovement. This information is captured by returning optical fibers inthe sensor probe, converted into an electrical signal and analyzed.

In an implementation, the system is both a tissue oximeter and laserDoppler flow meter. Therefore, the system can simultaneously determinemultiple parameters of a tissue, which may include a signal level ofreturned light, oxygen saturation level, total hemoglobin concentration,blood flow, pulse rate, and others.

FIG. 2 shows greater detail of a specific implementation of the systemof FIG. 1. The system includes a processor 204, display 207, speaker209, signal emitter 231, signal detector 233, volatile memory 212,nonvolatile memory 215, human interface device or HID 219, I/O interface222, and network interface 226. These components are housed within asystem unit enclosure. Different implementations of the system mayinclude any number of the components described, in any combination orconfiguration, and may also include other components not shown.

The components are linked together using a bus 203, which represents thesystem bus architecture of the system. Although this figure shows onebus that connects to each component, the busing is illustrative of anyinterconnection scheme serving to link the subsystems. For example,speaker 209 could be connected to the other subsystems through a port orhave an internal direct connection to processor 204.

A sensor probe 246 of the system includes a probe 238 and connector 236.The probe is connected to the connector using wires 242 and 244. Theconnector removably connects the probe and its wires to the signalemitter and signal detectors in the system unit. There is one cable orset of cables 242 to connect to the signal emitter, and one cable or setof cables 244 to connect to the signal detector. In an implementationthe cables are fiber optic cables, but in other implementations, thecables are electrical wires. In yet another implementation, the cablesinclude both fiber optic cables and electrical wires.

Signal emitter 231 is a light source that emits light at one or morespecific wavelengths. In a specific implementation, two wavelengths oflight (e.g., 690 nanometers and 830 nanometers) are used. In otherimplementations, other wavelengths of light may be used. The signalemitter is typically implemented using a laser diode or light emittingdiode (LED). Signal detector 233 is typically a photodetector capable ofdetecting the light at the wavelengths produced by the signal emitter.

Connector 236 may have a locking feature; e.g., insert connector, andthen twist or screw to lock. If so, the connector is more securely heldto the system unit and it will need to be unlocked before it can beremoved. This will help prevent accidental removal of the probe.

The connector may also have a first keying feature, so that theconnector can only be inserted into a connector receptacle of the systemunit in one or more specific orientations. This will ensure that properconnections are made.

The connector may also have a second keying feature that provides anindication to the system unit which type of probe is attached. Thesystem unit may handle making measurements for a number of differenttypes of probes. When a probe is inserted, the system uses the secondkeying feature to determine which type of probe is connected to thesystem. Then the system can perform the appropriate functions, use theproper algorithms, or otherwise make adjustments in its operation forthe specific probe type.

For example, when the system detects a probe with two optical fiber endsat its scanning surface is connected, the system uses probe algorithmsand operation specific for the two optical fiber probe. When the systemdetects that a probe with four optical fiber ends at its scanningsurface is connected, the system uses probe algorithms and operationspecific for the four optical fiber probe. When the system detects thata probe in a dilator is connected, the system uses dilator probealgorithms and operation. When the system detects that a probe in ahollow needle is connected, the system uses needle probe algorithms andoperation. A system can handle any number of different types of probes.There may be different probes for measuring different parts of the body,or different sizes or versions of a probe for measuring a part of thebody.

With the second keying feature, the system will be able to distinguishbetween the different probes. The second keying feature can use any typeof coding system to represent each probe including binary coding. Forexample, for a probe, there are four second keying inputs, each of whichcan be a logic 0 or 1. With four second keying inputs, the system willbe able to distinguish between sixteen different probes.

Probe 246 may be a handheld tool and a user moves the probe from onepoint to another to make measurements. However, in some applications,probe 246 is part of an endoscopic instrument, robotic instrument, apart of an instrument that inserts inside a body, or any combination ofthese. For example, the probe is moved or operated using a guidinginterface, which may or may not include haptic technology.

In various implementations, the system is powered using a wall outlet orbattery powered, or both. Block 251 shows a power block of the systemhaving both AC and battery power options. In an implementation, thesystem includes an AC-DC converter 253. The converter takes AC powerfrom a wall socket, converts AC power to DC power, and the DC output isconnected to the components of the system needing power (indicated by anarrow 254). In an implementation, the system is battery operated. The DCoutput of a battery 256 is connected to the components of the systemneeding power (indicated by an arrow 257). The battery is rechargedusing a recharger circuit 259, which received DC power from an AC-DCconverter. The AC-DC converter and recharger circuit may be combinedinto a single circuit.

The nonvolatile memory may include mass disk drives, floppy disks,magnetic disks, optical disks, magneto-optical disks, fixed disks, harddisks, CD-ROMs, recordable CDs, DVDs, recordable DVDs (e.g., DVD-R,DVD+R, DVD-RW, DVD+RW, HD-DVD, or Blu-ray Disc), flash and othernonvolatile solid-state storage (e.g., USB flash drive),battery-backed-up volatile memory, tape storage, reader, and othersimilar media, and combinations of these.

The processor may include multiple processors or a multicore processor,which may permit parallel processing of information. Further, the systemmay also be part of a distributed environment. In a distributedenvironment, individual systems are connected to a network and areavailable to lend resources to another system in the network as needed.For example, a single system unit may be used to collect results fromnumerous sensor probes at different locations.

Aspects of the invention may include software executable code orfirmware (e.g., code stored in a read only memory or ROM chip). Thesoftware executable code or firmware may embody algorithms used inmaking oxygen saturation measurements of the tissue. The softwareexecutable code or firmware may include code to implement a userinterface by which a user uses the system, displays results on thedisplay, and selects or specifies parameters that affect the operationof the system.

Further, a computer-implemented or computer-executable version of theinvention may be embodied using, stored on, or associated with acomputer-readable medium. A computer-readable medium may include anymedium that participates in providing instructions to one or moreprocessors for execution. Such a medium may take many forms including,but not limited to, nonvolatile, volatile, and transmission media.Nonvolatile media includes, for example, flash memory, or optical ormagnetic disks. Volatile media includes static or dynamic memory, suchas cache memory or RAM. Transmission media includes coaxial cables,copper wire, fiber optic lines, and wires arranged in a bus.Transmission media can also take the form of electromagnetic, radiofrequency, acoustic, or light waves, such as those generated duringradio wave and infrared data communications.

For example, a binary, machine-executable version, of the software ofthe present invention may be stored or reside in RAM or cache memory, oron a mass storage device. Source code of the software of the presentinvention may also be stored or reside on a mass storage device (e.g.,hard disk, magnetic disk, tape, or CD-ROM). The mass storage device maybe accessible via an Internet connection at a remote server (which maybe referred to as being stored on the “cloud”). As a further example,code of the invention may be transmitted via wires, radio waves, orthrough a network such as the Internet. Firmware may be stored in a ROMof the system.

Computer software products may be written in any of various suitableprogramming languages, such as C, C++, C#, Pascal, Fortran, Perl, Matlab(from MathWorks, www.mathworks.com), SAS, SPSS, JavaScript, AJAX, andJava. The computer software product may be an independent applicationwith data input and data display modules. Alternatively, the computersoftware products may be classes that may be instantiated as distributedobjects. The computer software products may also be component softwaresuch as Java Beans (from Sun Microsystems) or Enterprise Java Beans (EJBfrom Sun Microsystems).

An operating system for the system may be one of the Microsoft Windows®family of operating systems (e.g., Windows 95, 98, Me, Windows NT,Windows 2000, Windows XP, Windows XP x64 Edition, Windows Vista, Windows7, Windows CE, Windows Mobile), Linux, HP-UX, UNIX, Sun OS, Solaris, MacOS X, Google Chrome, Alpha OS, AIX, IRIX32, or IRIX64. Microsoft Windowsis a trademark of Microsoft Corporation. Other operating systems may beused, including custom and proprietary operating systems.

Furthermore, the system may be connected to a network and may interfaceto other systems using this network. The network may be an intranet,internet, or the Internet, among others. The network may be a wirednetwork (e.g., using copper), telephone network, packet network, anoptical network (e.g., using optical fiber), or a wireless network, orany combination of these. For example, data and other information may bepassed between the computer and components (or steps) of a system of theinvention using a wireless network using a protocol such as Wi-Fi (IEEEstandards 802.11, 802.11a, 802.11b, 802.11e, 802.11g, 802.11i, and802.11n, just to name a few examples). For example, signals from asystem may be transferred, at least in part, wirelessly to components orother systems or computers.

In an embodiment, through a Web browser or other interface executing ona computer workstation system or other device (e.g., laptop computer,smartphone, or personal digital assistant), a user accesses a system ofthe invention through a network such as the Internet. The user will beable to see the data being gathered by the machine. Access may bethrough the World Wide Web (WWW). The Web browser is used to downloadWeb pages or other content in various formats including HTML, XML, text,PDF, and postscript, and may be used to upload information to otherparts of the system. The Web browser may use uniform resourceidentifiers (URLs) to identify resources on the Web and hypertexttransfer protocol (HTTP) in transferring files on the Web.

FIG. 3 shows one implementation of a system 300 which includes amonitoring console 303 and a bone oximeter probe 305. The bone oximeterprobe includes a sensor head or unit 310 connected to an elongatedmember 315 connected to a cable 319. The sensor head includes one ormore distal ends of conductors (e.g., optical fibers, electrical wires,or both) which are located at a tip of the probe. The probe alsoincludes a connector 320 which includes proximal ends of the conductors.The conductors or optical fibers extend from the connector, through apassageway within the probe (i.e. within the cable and elongatedmember), to the sensor head. The connector is removably attached to areceptacle 325 which is affixed to or mounted on the monitoring console.

To use this probe to make measurements for a bone, a user, such as aphysician or surgeon, holds the elongated member and positions thesensor head to face or contact the bone to be measured. A signal istransmitted from the monitoring console, through the conductors, out thesensor head, and into the bone. The bone reflects a portion of thesignal which is received at the sensor head and transmitted through theconductors to the console. The console makes a calculation based on thesignal and reflected signal to determine a bone measurement. The bonemeasurement can then be displayed on an electronic display of theconsole. In a specific implementation, the bone measurement is an oxygensaturation parameter. The oxygen saturation parameter may be an oxygensaturation level value of the bone, a total hemoglobin concentrationvalue of the bone, or both.

Generally, the oxygen saturation parameter provides an indication of thehealth or vitality of the bone. The surgeon can then decide on aspecific course of action based on the health or oxygen saturationparameter of the bone. For example, in head and neck cancer surgery,tumors that occur in the jaw bone (i.e., oral cancers) may be radiatedand then resected. However, nonviable bone (often caused by radiationtreatment damage, known as radioosteonecrosis) is typically removedalong with the tumor. Removal of the nonviable bone may help to prevent,for example, infections. Therefore, information on what regions of thebone are nonviable can lead to reduced postoperative complications. Inother words, the oxygen saturation measurements provided by the systemcan help the surgeon determine the viable and nonviable regions of thebone so that the surgeon knows what specific portion of bone should beresected.

Further, a surgeon may also remove a portion of the healthy bonesurrounding the tumor or diseased bone to minimize the risk of possibleseeding. Seeding refers to the spreading of cancerous cells during tumorremoval. Using this bone oximeter, the surgeon can determine where thediseased bone ends and the healthy bone begins. The surgeon can thenresect the tumor along with a portion of the healthy bone that surroundsthe tumor.

The probe can be made of any suitable biocompatible material. The term“biocompatible material” is used in this application in its broadestsense and refers to a material which is used in situations where itcomes into contact with the cells, bodily fluids, or both of livinganimals and humans. It is desired that the selected biocompatiblematerial is chemically inert, and thermally and mechanically stable. Aprobe can be made of a metal (e.g., stainless steel, aluminum, andothers), a polymeric material, ceramic, plastic, or combinations ofthese.

In a specific implementation, the elongated member and sensor unit ofthe probe is made of metal. Some examples of metals include aluminum(e.g., 6061 aluminum), steel, stainless steel, and titanium. Theelongated member can be a tube (e.g., aluminum tube) that is hollow orhas a passageway to contain the conductors.

Sensor unit 310 includes distal ends of conductors such as opticalfibers. The distal ends of the conductors are arranged in a particularpattern (which are described more in detail in FIGS. 7 through 12), andmay include at least one source structure and at least one detectorstructure. A source structure is a structure in the sensor head thatprovides and transmits light into the bone or other tissue. The sourcestructure can generate light, or it can be a structural component thattransmits light generated elsewhere (e.g., from an upstream source). Adetector structure is a structure in the sensor unit that detects light(or that is a structural component of the detection process) which isscattered and reflected from the bone.

In one embodiment, a source structure can be a laser or light emittingdiode (LED) that emits a light of a specific wavelength suitable tomonitor oxygen saturation. A detector structure can be a photodiode(e.g., a PN diode, a PIN diode, or an avalanche diode) that detects thelight transmitted and reflected from a bone, after the source structureemits the light into the bone. In a sensor unit, both LEDs andphotodiodes can be located at the scanning surface of the sensor unit.These LEDs and photodiodes can then be electrically connected to asystem unit or console. In this embodiment, since the light is generatednext to the bone surface and subsequently detected at the bone surface,there is less attenuation of a signal as compared to otherimplementations where the LEDs and photodiodes are at the console.

In another embodiment, a source structure is an opening in a sensor unit(at its scanning surface) with an optical fiber inside, which isconnected to an emitter located elsewhere (e.g., system unit). Likewise,a detector structure is an opening in a sensor unit (at its scanningsurface) with an optical fiber inside, which is connected to a detectorlocated elsewhere. The optical fibers from each sensor unit are thenconnected to either an emitter or a detector which may be located in asystem unit or console.

This design can lower the cost of the probe because the emitters (e.g.,LEDs) and photodiodes are not a part of the probe. Rather, the emittersand photodiodes are external to the probe. Thus, the probe can be madeto be disposable and be cost-effectively replaced when it becomescontaminated such as after use (e.g., after one use).

In various other embodiments, a probe can have emitters and nophotodiodes, a probe can have photodiodes and no emitters, a probe canhave emitters and photodiodes, a probe can have some emitters whileother emitters are external to the probe, or a probe can have somephotodiodes while other photodiodes are external to the probe.

In embodiments of the invention, the cable contains conductors (e.g.,optical fibers) in a cable jacket and connects the sensor unit to aconnector which couples a sensor probe to a monitoring console. Thelength of the cable may vary. In a specific implementation, the lengthof the cable is about 3 meters, but can range from about 1.2 meters toabout 6 meters. For example, the cable may be about 1.5, 2, 2.5, 2.6,2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.5,5, 5.5, or 5.9 meters or more than 6 meters. Depending on the specificapplication, the cable length may be less than 1.2 meters. In someapplications, the cable length will be greater than 6 meters. It may bedesirable to use longer cables when a patient's immune system iscompromised and needs to be kept away from sources of contamination,such as a console.

In an implementation, the cable includes one or more optical wave guidesenclosed in a flexible cable jacket. The optical wave guides may be usedto transmit light from the console, through the sensor unit and into thebone. The optical wave guides may also be used to transmit the lightreceived from the bone back to the console.

The optical wave guides may have the shape of a polygon, such as asquare, rectangle, triangle, or other shape. In other cases, the opticalwave guides may have circular or oval shapes. In a specificimplementation, the optical wave guides are multiple strands of fiberoptic cable or optical fiber. The flexible cable jacket may be made ofpolyvinyl chloride (PVC) such as thin-walled PVC with or without analuminum helical monocoil, shrink wrap tubing, plastic, rubber, orvinyl.

In a specific embodiment, all of the fiber optic cables are enclosedwithin one end, or both ends of the flexible cable jacket. Minimizingthe number of exposed cables lowers the likelihood that the cables willget entangled. In another embodiment, the fiber optic cables are notenclosed together and instead each fiber optic cable is enclosed in itsown flexible cable jacket.

In a specific implementation, the cable is passive. For example, it willnot contain any active, generative properties to maintain signalintegrity. However, in other implementations, the cable may includeactive components. The cable may include active components to amplifythe signal transmitted through the sensor unit, received at the sensorunit, or both. For example, long lengths of cable subject to significantattenuation may benefit from amplification. Amplification may also beused if the monitored site contains a particularly dense structure suchas bone. In a specific implementation, radiation sources such as lightemitting diodes (LEDs) may be placed in the sensor unit. Thus, the cablemay contain electrical wiring to transmit power to the radiationsources.

In an embodiment of the invention, each opening on the sensor unit andcorresponding cable is dedicated to a particular purpose. For example, afirst opening on the sensor unit (and corresponding fiber optic cable)is dedicated to transmitting light from the monitoring console. A secondopening on the sensor unit is dedicated to transmitting a signalreceived at the second opening to the monitoring console.

Some embodiments use a particular opening and cable for multiplepurposes (e.g., both input and output) using a scheme such asmultiplexing.

In a specific embodiment, a particular opening and cable transmits anoutput to affect a reaction (e.g., sending electrical signals tostimulate muscle, nerve, or other tissue). Another opening and cabletransmits the resultant signal back to the monitoring device. In yetanother embodiment, the openings and cables may simply detect changesand transmit these changes back to the monitoring device. For example,the openings and cables may carry voltage changes in the patient'stissue back to the monitoring device.

Connector 320 at the end of the cable attaches the sensor probe to itsreceptacle on the console. The connector also protects the cable fromaccidental disconnection. The connector may include a collar thatthreads onto the receptacle on the console. Alternatively, the connectormay include a lug closure, press-fit, or snap-fit components.

In a specific implementation, the console can provide alerts to the userwhen a proper connection is made between the sensor probe and theconsole. The alerts may be visual (e.g., a flashing light on a displayof console), audible, or both. The display monitor may also show a typeof sensor device (e.g., bone oximeter device, dilator sensor device,needle sensor device, and others) that is attached to the console, aswell as other information.

In a specific implementation, there may be other connectors on the cablebesides connector 320. These other connectors allow the cable to beseparated into two or more pieces. Additional lengths of cable can beadded to one or both pieces to increase the overall length of the cableor portions of the cable can be removed to shorten the overall length ofthe cable. Furthermore, having multiple connectors allows disconnectingof a contaminated portion of the cable from an uncontaminated portion ofthe cable. The contaminated portion of the cable, rather than the entirelength of cable, can be disposed and new cable can then be connected tothe uncontaminated portion of the cable. This can save money because theentire length of the cable is not being discarded after one-use.

In one implementation, console 303 (sometimes referred to as amonitoring console or system unit) shown in FIG. 3 can be a portableconsole which may be hand carried. A portable console can follow apatient and optical measurements can be made anywhere in the hospital.In this implementation, it is desirable that the portable console isbattery operated. In another implementation, the console may be a large,nonportable device that is attached to a wall or secured to a stand. Inthis implementation, the system is typically connected to AC power.

The console may include a mass storage device to store data. Massstorage devices may include mass disk drives, floppy disks, magneticdisks, optical media, phase-change media, fixed disks, hard disks,CD-ROM and CD-RW drives, DVD-ROM and DVD-RW drives, flash and othernonvolatile solid-state storage drives, tape storage, reader, and othersimilar devices, and combinations of these.

The stored data may include patient information. This includes, forexample, the patient's name, social security number, or otheridentifying information, measurements of light returned from thepatient's tissue, oxygen saturation, total hemoglobin concentration,blood flow, pulse, signal quality, and the time and date ofmeasurements. The measurements of various physiological parameters mayinclude high, low, and average values and elapsed time betweenmeasurements.

The above drives may also be used to update software in the console. Theconsole may receive software updates via a communication network such asthe Internet.

In an implementation, the console also includes an interface fortransferring data to another device such as a computer. The interfacemay be a serial, parallel, universal serial bus (USB) port, RS-232 port,printer port, and the like. The interface may also be adapted forwireless transfer and download, such as an infrared port. The systemtransfers data without interruption in the monitoring of the patient.

The console also includes a display screen (e.g., electronic display)which may display the patient's data, such as measurements of lightreturned from the patient's tissue, oxygen saturation, total hemoglobinconcentration, blood flow, pulse, signal quality, or any combinations ofthese parameters. The screen may be a flat panel display or include atouch screen interface so that the user can input data into the console.

The console, in addition to the display, may also include a processor,signal emitter circuit, signal detector circuit, and a receptacle toremovably couple ends of one or more conductors. In a specificimplementation, the ends of one or more conductors (e.g., optical fibersor electrical wires) are instead permanently connected to the console.The signal emitter circuit may operate to send a signal through the oneor more conductors. The signal detector circuit then receives a signalvia one or more conductors.

In a specific implementation, the signal emitter circuit may include oneor more laser emitters, light emitting diode (LED) emitters, or both.The signal emitter circuit may be used to generate an optical signalhaving two or more different wavelengths to be transmitted through thesensor unit. The wavelengths may range from about 600 nanometers toabout 900 nanometers.

In a specific implementation, the console includes first and secondradiation sources. The radiation sources may be dual wavelength lightsources. That is, the first and second radiation sources each providetwo wavelengths of radiation. The first radiation source, secondradiation source, or both may include one or more laser diodes or lightemitting diodes (LEDs) that produce light in any wavelength, buttypically the wavelengths range from about 600 nanometers to about 900nanometers. In a specific implementation, the first and second radiationsources generate a first wavelength of light that is about 690nanometers and a second wavelength of light that is about 830nanometers.

In a specific implementation, one or more near-infrared radiationsources are included within the console. In other implementations, theradiation sources may be external to the console. For example, theradiation sources may be contained within a separate unit between theconsole and sensor probe. The radiation sources may, for example, becontained in a sensor probe or sensor unit itself or in other parts(e.g., in the console). In yet another implementation, some radiationsources may be within the console while other radiation sources areexternal to the console.

These radiation sources may be near-infrared lasers. In a specificimplementation, there is one near-infrared laser located within theconsole. In other implementations, there may be more than onenear-infrared laser. For example, there may be 2, 3, 4, 5, 6, 7, 8, 9,or 10, or more than 10 radiation sources. In another implementation, theradiation sources may include those that produce a visible light.

Also, in a specific implementation only a percentage of the power outputof the source is transmitted to the tissue. For example, when the laserdiode output is 30 milliwatts, the power that gets to the tissue may beabout 3 milliwatts. So, approximately 1/10 of the power of the laserdiode is transmitted into the tissue.

In a specific implementation, a single pulse of light is transmittedinto the tissue. In another implementation, multiple pulses of light maybe transmitted into the tissue. For example, a first pulse of light maybe received by a first detector. A second pulse of light may be receivedby a second detector.

FIG. 4 shows a specific implementation of a measuring or monitoringsystem in accordance with the present invention. As shown, a sensorprobe 405 (e.g., a sensor probe which is a part of a bone oximeterdevice) is connected to a system unit 410. The system unit includes asignal emitter 415, a signal detector 420, an analog-to-digitalconverter 425, an oximeter analyzer 430, a Doppler effect analyzer 435,and a number of output parameters. These output parameters include asignal quality factor 440, a signal level of returned light 445, a totalhemoglobin concentration 450, an oxygen saturation level 455, a bloodflow 460, and a pulse 465.

These components may be housed within a single housing. Alternatively,these components may be housed in separate housings. Differentimplementations of the system may include any number of the componentsdescribed, in any combination or configuration, and may also includeother components not shown.

Signal emitter 415 emits light of a suitable wavelength or wavelengthsinto sensor probe 405 through source fibers into a bone where opticalmeasurements are desired. When light is transmitted to a target bone viasource structures in the sensor unit, light scatters due to theheterogeneous structure of the bone, and some of the light is absorbedby chromophores such as hemoglobin. An attenuated version of the lightthat is reflected by the bone is detected by detector structures in thesensor unit and is transmitted to signal detector 420 in the systemunit. Also, due to Doppler effect, the frequency of the reflected lightis broadened and the frequency of the reflected light will be broaderthan the frequency spectrum of the original light. These changes arealso detected by signal detector 420. As shown in FIG. 4, signaldetector 420 may be connected to analog-to-digital converter 425 whichin turn may be connected to oximeter analyzer 430, Doppler effectanalyzer 435, or both.

From optical measurements obtained from the signal detector, a signalquality factor 440 (sometimes referred to as a Q factor in otherapplications) can be obtained. The signal quality factor is a parameterthat is associated with the ratios of optical measurements from thesensor head. The calculated signal quality factor can vary from 0 to 1(sometimes scaled and displayed from 0 to 100). When the signal qualityfactor is approximately 1 (or 100 when scaled up), this indicates thatthe sensor unit is in good contact with bone, that the bone is highlyhomogeneous, and that the sensor probe is in good working order. Thesignal quality factor can indicate the quality of signal obtained fromthe signal detector. Discussions of a Q factor or a signal qualityfactor can be found in U.S. patent application Ser. No. 11/162,380,filed Sep. 8, 2005, which is incorporated by reference.

The changes in the intensity and frequency spectrum of returned light isanalyzed by oximeter analyzer 430 and Doppler effect analyzer 435. Fromthese analyses, a number of different parameters can be calculated. Oneor combinations of parameters will help a surgeon to determine thehealth of the tissue or bone.

Oximeter analyzer 430 calculates oxygen saturation level or value (StO₂)455, hemoglobin concentration (deoxyhemoglobin, oxyhemoglobin, or totalhemoglobin) 450, or both. The calculations are based on a value of theinitial light generated by the signal emitter and a value of anattenuated version of the light that is reflected from the bone and issubsequently detected by the signal detector. The term oxygen saturationlevel (or value) refers to the percentage of hemoglobin that is bound tooxygen at the time of measurement. Additional details on attenuationmethods are also discussed in U.S. patent application Ser. No.12/126,860, filed May 24, 2008, which is incorporated by reference. Theattenuation ratio method may also include techniques discussed in U.S.Pat. No. 6,587,701, which is incorporated by reference.

In the automatic error-cancellation or self-calibration scheme, thesystem factors such as source intensity, detector gain, and loss oflight in the optical fibers and connectors are cancelled automatically.The automatic error-cancellation scheme is discussed in more detail asequations 5a and 5b in U.S. Pat. No. 6,597,931, which is incorporated byreference. The self-calibration scheme may also include equationsdiscussed in U.S. Pat. Nos. 6,516,209, 6,735,458, and 6,078,833, U.S.patent application Ser. No. 12/126,860, filed May 24, 2008, and NewOptical Probe Designs for Absolute (Self-Calibrating) NIR TissueHemoglobin Measurements, Proc. SPIE 3597, pages 618-31 (1999), which areincorporated by reference.

Generally, bones, like other tissues, use the oxygen and nutrients thatblood supplies. Healthy bones can be distinguished from unhealthy bonesusing the sensor measurements provided by the system. For example,unhealthy bones can have inadequate blood perfusion. Thus, an indicationof bone health can be determined by measuring bone oxygenation.Specifically, healthy bones can have a higher number of blood cells (andthus a higher concentration of hemoglobin) and be more richly oxygenatedas compared to unhealthy bones.

The signal level of returned light can be used as an indicator ofwhether a bone is healthy or unhealthy. A healthy bone or a bone that iswell-perfused will absorb infrared and visible red light more than theunhealthy bone.

In a specific implementation, the system includes a laser Doppler todetect regions of high versus low blood flow. Such information canindicate whether or not perfusion is adequate (e.g., bony bleeding).Doppler effect analyzer 435 can calculate blood flow 460 and pulse 465.The Doppler effect analyzer analyses the intensity and spectrum changeof light when it is transmitted and reflected from a bone. Laser lightis scattered by the red blood cells in the capillaries and the tissuesurrounding the capillaries. The velocity of the blood flow, which runsin all directions in the capillary network, has velocity distributionaveraging at 1 millimeter per second or less. The tissue scatteringcross section is much greater than that of the moving red blood cells.Based on this information, the following calculations can be obtained.

The fluctuating intensity of the light that is scattered to thedetector, i.e. the signal, can be written as

$\begin{matrix}{{{P(\omega)} = {{i_{0}^{2}{\delta(\omega)}} + \frac{C\; i_{0}}{\pi} + {i_{0}^{2}{S(\omega)}}}},} & (1)\end{matrix}$

where i₀ is the mean detected intensity, S(ω) is the spectrum, and C isa constant.

The first moment of S(ω) is the mean Doppler shift,

$\begin{matrix}{\left\langle \omega \right\rangle = {\int_{- \infty}^{\infty}{{\omega }{S(\omega)}\ {{\mathbb{d}\omega}/{\int_{- \infty}^{\infty}{{S(\omega)}\ {{\mathbb{d}\omega}.}}}}}}} & (2)\end{matrix}$

The mean Doppler shift is proportional to the rms speed of the movingparticles

$\sqrt{\left\langle V^{2} \right\rangle}$as

$\begin{matrix}{\left\langle \omega \right\rangle = {{F\left( {\left\langle V^{2} \right\rangle^{1/2},a,\overset{\_}{m}} \right)} = {\left\langle V^{2} \right\rangle^{1/2} \times \frac{1}{a} \times \left\lbrack {\frac{1}{\left( {12\;\zeta} \right)^{1/2}}\beta\;{f\left( \overset{\_}{m} \right)}} \right\rbrack}}} & (3)\end{matrix}$

where V is the velocity of the moving RBC, a represents the size of thescatter (i.e. the radius of spherical scatter or radius of RBC disc), ξis an empirical factor which is related to the shape of the cells,β=0.17 is a constant, m is the mean number of scattering of photon withRBC, and

$f\left( \overset{\_}{m} \right)$is a function of m only.

$f\left( \overset{\_}{m} \right)$can be expressed as follows

$\begin{matrix}{{f\left( \overset{\_}{m} \right)} = {{\frac{2}{\pi^{1/2}}{\exp\left( {{- 2}\overset{\_}{m}} \right)}{\sum\limits_{j = 1}^{\infty}\frac{\left( {2\;\overset{\_}{m}} \right)^{j}{\Gamma\left( {j + {1/2}} \right)}}{{\Gamma\left( {j + 1} \right)}{\Gamma(j)}}}} \propto \left\{ {\begin{matrix}\overset{\_\;}{m} & {{{if}\mspace{14mu}\overset{\_}{m}} \leq 1} \\\left( \overset{\_}{m} \right)^{1/2} & {{{if}\mspace{14mu}\overset{\_}{m}} \geq {2m}}\end{matrix}.} \right.}} & (4)\end{matrix}$

It is noted that the typical values of the quantities in Eq. (3) are asfollows: V˜0.2-2.0 mm/sec, a<0.15 μm, m˜1.2ξ˜0.1 and β=0.17.

The mean number m of scattering of photon with RBC in (3) should beproportional to the total hemoglobin concentration. Replacing m by Hgb,we have

$\begin{matrix}{\left\langle V^{2} \right\rangle^{1/2} \propto {\left\langle \omega \right\rangle \times \left\{ {\begin{matrix}{Hgb} & {\;{{if}\mspace{14mu}{Hgb}\mspace{14mu}{small}}} \\{Hgb}^{1/2} & {{if}\mspace{14mu}{Hgb}\mspace{14mu}{large}}\end{matrix}.} \right.}} & (5)\end{matrix}$

By using the above equations as a guide for calibration, the blood flowcan be calculated. The pulse can also be derived from Doppler blood flowmeasurements. Some general discussions of Doppler flowmetry andestimating blood flow can be found in P. Elter et al., “Noninvasive,real time laser Doppler flowmetry in perfusion regions and largervessels”, SPIE Proceeding Vol. 3570, pages 244-54, Stockholm, Sweden,1998; R. Bonner et al., “Model for laser Doppler measurements of bloodflow in tissue”, Applied Optics, Vol. 20, No. 12, 1981. Thesepublications are incorporated by reference in this application.

The blood flow may also be calculated using laser Doppler flowmetry(LDF). The flow curve obtained may be noisy, and a smooth filtering maybe applied to the flow curve before calculating a pulse rate from theflow curve. The Savitzky-Golay (S-G) smoothing filter in time domain maybe applied to the data obtained in the flow curve. The S-G filter isdescribed in Savitzky and Golay, Analytical Chemistry, Vol. 36, pp.1627-39 (1964), which is incorporated by reference in this application.

The S-G filter is applied to a series of equally spaced data valuesf_(i)≡f(t_(i)), where t_(i)≡t₀+iΔ, for some constant sample time spacingΔ and i= . . . −2, −1, 0,1, 2, . . . . The S-G filter replaces eachf_(i) by a linear combination g_(i) of itself and some number of nearbyneighbors,

$\begin{matrix}{g_{i} = {\sum\limits_{n = {- n_{L}}}^{n_{R}}{c_{n}f_{i + n}}}} & (6)\end{matrix}$

In equation (6), n_(L) is the number of points used “to the left” of adata point i (i.e., earlier than it), while n_(R) is the number used tothe right (i.e., later). The S-G filter approximates the underlyingfunction within the moving window by a polynomial, typically quadratic(the 1^(st) order) or quartic (the 2^(nd) order). For each point f_(i),it least-squares fits a polynomial to all n_(L)+n_(R)+1 points in themoving window, and then set g_(i) to be the value of that polynomial atpoint i. The 0-th order S-G filter is also called moving windowaveraging, which, by letting g_(i) in equation (6) be a linearcombination of f_(i)s with equal weight, i.e., settingc_(n)=1/(n_(L)+n_(R)+1).

The pulse rate can be calculated from the flow curve in time domain byusing the following steps. The S-G filter is used to smooth the bloodflow curve (i.e., a graph of sample time points on X-axis and blood flowin arbitrary units on the Y-axis), resulting in a secondary smoothedflow curve. In an implementation, this S-G filter may be of 0-th orderand with n_(R)=0. In some other embodiments, a higher-order S-G filtermay be used.

Then the time difference between any two adjacent peaks of the smoothedflow curve is determined. This time difference is the pulse duration.The pulse duration may then be converted into a pulse rate. Finally, theaverage pulse rate can be calculated among given number of pulse rates.The average pulse rate can then be used to determine whether the bone ishealthy or unhealthy.

A suitable sampling rate can be selected to measure various parametersof the tissue. For monitoring multiple parameters (including oxygensaturation level, hemoglobin concentration, signal level of returnedlight, blood flow and pulse rate), the system or console may include ananalog-to-digital converter 425 for fast data sampling desired for bloodflow measurement. For measuring blood flow and pulse, at least one ofthe radiation sources is continuously on while one of the detectorscollects signals at a fast sampling rate. For example, a sampling rateof about two kilohertz (i.e., one sampling per half second) may be usedto determine oxygen saturation level or hemoglobin concentration ofbone. On the other hand, a sampling of about 100 kilohertz (i.e., onesampling per 0.01 millisecond) may be used to determine the blood flowand pulse rate of bone.

As an illustration, to obtain an oxygen saturation level and a totalhemoglobin concentration, a software in the console may send an “X”command to collect oximeter raw data (e.g., intensity of returned lightat all the detectors after each of the source emitted) by sampling, forexample, once each 10 seconds. In addition, the software may sendmultiple “C” commands. The “C” commands may send additional 150emissions via laser diode S1 (at 830 nanometers once every 0.07 seconds)between two successive X commands to measure the blood flow and pulse.The signals from additional laser Doppler flowmetry emissions receivedby one of the photodiodes (e.g., detector structure D2) may be, with amuch higher rate (e.g., 25 kilohertz), transferred to digitalinformation and may be recorded in a separate data file for furtheranalysis. These sampling rates are exemplary, and other suitablesampling rates may be used to collect data.

Any one or combinations of parameters described above can be combined toformulate an overall indicator or index for the health of the bone. Inone implementation, the signal level of returned light and blood flowparameters may be combined to formulate an indicator for bone health. Inanother implementation, the signal level of returned light, totalhemoglobin concentration, and blood flow parameters may be combined toformulate an indicator for bone health. In yet another implementation,total hemoglobin concentration, blood flow, and pulse parameters may becombined to formulate an indicator for bone health. In yet anotherimplementation, all five parameters (i.e., the signal level of returnedlight, total hemoglobin concentration, oxygen saturation level, bloodflow, and pulse) may be combined to formulate an indicator for bonehealth.

FIG. 5 shows a specific implementation of a bone oximeter probe 505.FIG. 6 shows a longitudinal cross section of a tip of the bone oximeterprobe shown in FIG. 5. Bone oximeter probe 505 includes an elongatedmember 510, a sensor unit 515 at the tip of the elongated member, and acable 520 extending from the elongated member to a connector 530. InFIG. 5, a portion of the probe is shown cutaway to show optical fibers525 which extend through a passageway or lumen in the probe.

In a specific implementation, an algorithm to make bone oximetermeasurements uses a probe with four optical fibers. That is, each of thefour optical fibers extend from the connector, through the cable,through the elongated member, and to the sensor unit. The ends of thefibers are exposed on a surface of the sensor unit. In this specificimplementation, two of the four optical fibers are source fibers whilethe other two optical fibers are detector fibers. This configuration ofthe four fibers may be referred to as a 2s2d configuration (i.e., 2source fibers and 2 detector fibers). This allows for one 2-source and2-detector pair for making measurements using the algorithm.

In another specific implementation, an algorithm to make bone oximetermeasurements uses a probe with six optical fibers. Similar to the 2s2dconfiguration, each of the six optical fibers extend from the connector,through the cable, through the elongated member, and to the sensor unitwhere ends of the fibers are exposed on the surface of the sensor unit.In this specific implementation, two of the six optical fibers aresource fibers while the remaining four optical fibers are detectorfibers. This configuration of the six fibers may be referred to as a2s4d configuration (i.e., 2 source fibers and 4 detector fibers). Thisallows for six 2-source and 2-detector pairs for making measurementsusing the algorithm. For example, if the two sources are identified as51 and S2, and the four detectors are identified as D1, D2, D3, and D4,a first pair is S1/S2 and D1/D2. A second pair is S1/S2 and D1/D3. Athird pair is S1/S2 and D1/D4. A fourth pair is S1/S2 and D2/D3. A fifthpair is S1/S2 and D2/D4. A six pair is S1/S2 and D3/D4.

In this specific implementation of the 2s4d configuration, the algorithmuses a weighted average for the six oxygenation (StO2) values given byeach of the six 2-source and 2-detector pairs. So, one benefit of the2s4d configuration is that a measurement (e.g., an StO2 output) can bemade even if one or more of the six 2-source and 2-detector pairs isunable to make a measurement. For example, there may be debris on thesensor head which affects one or more of the six pairs, there may beimproper or not good contact with one or more of the six pairs and thebone surface, and so forth.

A benefit of the 2s2d configuration is that it allows for a smallersensor head (e.g., small sensor head surface) since the sensor head hasfour fibers instead of six fibers. Small sensor heads are generallydesirable because they can be used with small incisions in soft tissueto gain access to the underlying bone. With a small incision, there istypically less cutting of the patient's tissue, less blood loss, lesspain, less scaring, less risk of infection, and so forth as compared toa large incision. Thus, depending upon the specific surgical scenario adoctor may select the 2s2d configuration over the 2s4d configuration orvice versa. In making the selection, the doctor may weigh factors suchas the depth of the bone within the soft tissue, size of the bone to bemeasured, the patient's health, and other factors.

In various other implementations, the algorithm can be adapted to useany number of source and detector fibers. Some examples of other sourceand detector fiber configurations include 1s1d (one source and onedetector fiber), 1s2d (one source and two detector fibers), 1s3d (onesource and three detector fibers), 2s1d (two source and one detectorfiber), 2s3d (two source and three detector fibers), 4s4d (four sourceand four detector fibers), and so forth. A number of source fibers in aprobe may equal a number of detector fibers such as in the 2s2dconfiguration. A number of source fibers in a probe may be less than anumber of detector fibers such as in the 2s4d configuration. A number ofsource fibers in a probe may be greater than a number of detectorfibers.

The sensor unit includes distal ends of the optical fibers. Connector530 connected to an end of the cable includes proximal ends of theoptical fibers. The cable encases the optical fibers in a cable jacket.In FIG. 5, the connector is shown disassociated or exploded to showproximal end portions of the optical fibers. In the embodiment shown inFIG. 5, the optical fibers run continuously from the sensor unit to theconnector. However, in other embodiments, the optical fibers may beinterrupted by, for example, an amplifier, beam combiner, or otherdevice between the sensor unit and connector.

Typically, the elongated member will be made to be rigid or made of arigid material. This allows the user to hold the elongated member withthe sensor head against the bone without having the elongated membercollapse. In a specific implementation, elongated member 510 is a hollowmetal tube, such as an aluminum tube. However, the elongated member canbe made of any material (e.g., plastic). In this specificimplementation, the tube has a circular cross section. However, thecross section can have any shape (e.g., square, rectangle, oval, orellipse).

Lengths L3 and L5 indicate lengths of the elongated member and cable,respectively. In a specific implementation, length L5 is greater thanlength L3. However, length L5 may be less than or equal to length L3. Touse the probe, the surgeon (or a robot) holds the elongated member. Theelongated member thus has a length that permits it to be held such as bythe hand of the surgeon. In a specific implementation, length L3 isabout 200 millimeters and length L5 is about 3000 millimeters. But,length L3 can range from about 100 millimeters to about 500 millimeters.This includes, for example, 125, 150, 175, 225, 250, 275, 300, 325, 350,375, 400, 425, 450, 475, or 499 millimeters. Length L3 may be less than100 millimeters or greater than 500 millimeters.

A probe having a long elongated member can be inserted further into softtissue to reach the underlying bone as compared to a probe having ashort elongated member (FIG. 28). However, if the elongated member istoo long, it may be difficult and awkward to position and manipulate theprobe. Thus, selecting an elongated member having the desired length candepend on factors such as the distance between the target location onthe bone to be measured and the location of the incision in the softtissue for the probe to be inserted.

In a specific implementation, length L3 of the elongated member isfixed. That is, the length is not adjustable by the user. In anotherimplementation, length L3 is adjustable. In this specificimplementation, the elongated member includes a series of telescopingsections with each section having a progressively smaller width ordiameter. To lengthen the elongated member, the user holds a firsttelescoping section and pulls a second telescoping section away from thefirst telescoping section. This allows the second telescoping section toextend away from the first telescoping section. To shorten the elongatedmember, the user holds the first telescoping section and pushes thesecond telescoping section towards the first telescoping section. Thiscollapses the second telescoping section into the first telescopingsection.

In another implementation, the length of the elongated member isadjusted by connecting or disconnecting one or more sections of theelongated member. In this specific implementation, the elongated memberincludes a set of connectable sections. To lengthen the elongatedmember, the user can connect two or more sections of the elongatedmember together (e.g., push together and twist). To shorten theelongated member, the user can disconnect and remove one or moresections (e.g., untwist and pull).

In a specific implementation, the elongated member is straight. That is,the elongated member does not have any bends, angles, curves, or changesin direction.

In another implementation, the elongated member is not straight. Forexample, the elongated member may have one or more angles or bends tohelp the surgeon position the probe against the bone to be measured. Inthis specific implementation, the elongated member includes a joint thatconnects a first section to a second section of the elongated member. Anangle is between the first and second section

In a specific implementation, the angle or joint is fixed and can not beadjusted by the user. An angle between two sections of the elongatedmember may be about 30, 40, 45, 60, or 90 degrees. The angle can rangefrom about 90 degrees to about 179 degrees. The angle can be less than90 degrees or more than 179 degrees.

In another implementation, the angle or joint is adjustable. In thisspecific implementation, the user can hold the first section and move orpivot the second section relative to the first section to adjust theangle between the first and second sections. The joint between the twosections may be lockable so that the first and second sections do notaccidentally move.

The joint can be made to have any number of degrees of freedom. Thejoint may be a hinge so that the sections can move up and down, but notleft and right. The joint may be a ball and socket mechanism where oneof the first or second sections includes the ball and another of thefirst or second sections include the socket. This allows, for example,the first section to move, relative to the second section, up and down,and left and right.

In another specific implementation, the elongated member or a portion ofthe elongated member is bendable. For example, the elongated member maybe implemented as a gooseneck or a flexible jointed metal pipe. Thegooseneck can be manually bent or adjusted into any desiredconfiguration so as to avoid interference with, for example, otherinstruments in the operating area.

Cable 520 will typically be made to be flexible or made of a flexiblematerial. This allows the probe to be routed around various structuresor instruments in the surgical area. In a specific implementation, thecable length (i.e., length L5) is about 3000 millimeters. Length L5 canrange from about 1000 millimeters to about 6000 millimeters. Thisincludes, for example, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000,5500, or 5999 millimeters. Length L5 may be less than 1000 millimetersor greater than 6000 millimeters.

As shown in FIG. 5, a portion 539 of the cable is inserted into theelongated member (i.e., is inserted into a proximal end 538 of theelongated member). That is, at least a portion 540 of the elongatedmember overlaps a portion of the cable. In this specific implementation,the cable and elongated member have circular cross sections. An outerdiameter of the cable is less than an inner diameter of the elongatedmember so that the cable can be inserted or fitted into the elongatedmember.

The cable may be inserted any distance into the elongated member. Forexample, the cable may be inserted into the elongated member such thatan entire length of the elongated member overlaps the cable. That is,the cable extends through the elongated member and to the sensor head.The cable may be partially inserted into the elongated member such thatthe cable terminates before reaching the sensor head. For example, thecable may be inserted into the elongated member such that it terminatesat a midpoint of the length of the elongated member. The cable may beinserted into the elongated member such that it extends into theelongated member for about three-quarters, one-half, one-third,one-quarter, one-eighth, or one-sixteenth of the length of the elongatedmember.

In a specific implementation, a length of the elongated member is about200 millimeters. In various implementations, the cable is inserted to adepth of about 150 millimeters within the elongated member, i.e.,three-quarters the length of the elongated member. That is, a length ofthe cable from proximal end 538 of the elongated member to an end 541 ofthe cable is about 150 millimeters. The cable can extend any depth ordistance into the elongated member. The depth can range from about 10millimeters to about 200 millimeters (i.e., the entire length of theelongated member). This includes, for example, about 12, 20, 25, 30, 40,50, 60, 67, 70, 80, 90, 100, 110, 120, 130, 140, 160, 170, 180, 190, or199 millimeters. The depth of insertion may be less than 10 millimetersor greater than 199 millimeters. Generally, the further the cable isinserted into the elongated member, the less likely it is that the cableand elongated member can separate accidentally. For example, there willbe a greater amount of surface area for bonding between the elongatedmember and the cable. However, longer lengths of cable can increasecosts. Therefore, the cable is typically inserted into the elongatedmember to a depth or distance sufficient to prevent accidentalseparation during normal use.

Securing the cable and elongated member together by inserting the cableinto the elongated member can help eliminate the need for anothercomponent such as a coupler between the cable and elongated member tosecure the cable and elongated member together. Eliminating a componentcan reduce the cost of the probe.

In other implementations, the elongated member is inserted into thecable and at least a portion of the cable overlaps a portion of theelongated member. The elongated member may inserted into the cable suchthat the cable overlaps the entire length of the elongated member andthe elongated member is not visible. The elongated member may bepartially inserted into the cable so that a portion of the elongatedmember not inserted into the cable is visible.

Any technique may be used to secure the elongated member and cabletogether. In a specific implementation, an adhesive such as epoxy isused to attach the cable to the elongated member. In this specificimplementation, a portion of the cable is coated with a layer of theadhesive. The cable is then inserted into the elongated member and theadhesive dries or cures to secure the cable and elongated membertogether.

In another specific implementation, friction between the surface of theelongated member (i.e., inner surface) and the surface of the cable(i.e., outer surface) is used to help prevent the elongated member andcable from separating. The elongated member may include threads (i.e.,internal or female threads) so that the elongated member can be screwedto twisted onto the cable. As the elongated member is twisted on thethreads of the elongated member may cut corresponding threads onto thecable.

In another implementation, one of the elongated member or cable is notinserted into another of the elongated member or cable. Rather, in thisspecific implementation, the ends of the elongated member and cable arebutted together. For example, an end of the elongated member may beglued, welded, taped, or fused to an end of the cable. The end of theelongated member may have a barbed connector so that the end of thecable can be pushed and stretched over the barbed connector. In aspecific implementation, a coupling device is used to connect theelongated member and cable together. The coupling device has a first endand a second end, opposite the first end. The first end receives an endof the elongated member and the second end receives an end of the cable.

As shown in FIG. 6, a tip 537 of the bone oximeter probe has sensor unit515 (sometimes referred to as a sensor head) which includes a block 610with four channels or holes extending along the longitudinal axis of theblock. The distal end portions of optical fibers 525 a, 525 b, 525 c,and 525 d are inserted into each channel in the block. An adhesive, suchas epoxy, may be used to secure or attach the optical fibers to thechannels in the block.

The channels in the block separate and fix distal ends of the opticalfibers by a suitable distance to optimize optical measurements for agiven bone. There can be any number of channels in the block (e.g., one,two, three, four, five, six, or more than six channels). The block mayextend the entire length of the elongated member; alternatively, theblock may be present only at the distal end of the probe (or elongatedmember), as shown in FIG. 6, to firmly fix the distal end portions ofthe optical fibers.

Any suitable material can be used for the block as long as it ischemically and structurally stable, and does not interfere withtransmission of optical signals in the optical fibers. For example, theblock can be made of an aluminum alloy (e.g., 6061 aluminum alloy) withchannels for threading optical fibers through. Then the aluminum alloyblock can be attached to the inner surface of the elongated member atthe tip using an adhesive, such as Epotek 353ND epoxy.

The block can be attached to the elongated member using other attachmentmechanisms instead of or in addition to an adhesive. For example, theblock and elongated member may have threads so that the block can bescrewed into the elongated member. The block may be attached to theelongated member using a press fit or interference fit. The block may bewelded or brazed to the elongated member. The block may be integrallyformed with the elongated member as a single unit, such as via injectionmolding using a single mold to form the elongated member and block.

Although FIGS. 5 and 6 show the block inserted into the elongated memberor inside the elongated member, the block or a portion of the block maybe outside the elongated member. For example, the block may be a capwhich fits over the tip of the elongated member. The cap can havechannels for holding the fiber optic cables.

FIG. 6 shows some dimensions of the probe tip. In a specificimplementation, the block and elongated member are cylindrical in shape.That is, cross sections of the block and elongated member have the shapeof a circle. Diameters D1 and D2 indicate outer and inner diameters,respectively, of the elongated member. A diameter D3 indicates adiameter of the block. A length L10 indicates a length of the block.

In this specific implementation, diameter D1 is about 7 millimeters, butcan range from about 4 millimeters to about 14 millimeters. Thisincludes, for example, 4.5, 5, 5.5, 6, 6.5, 7.5, 8, 8.5, 9, 9.5, 10,10.5, 11, 11.5, 12, 12.5, 13, 13.5, or 13.9 millimeters. Diameter D1 maybe less than 4 millimeters or greater than 14 millimeters.

In a specific implementation, diameter D2 is about 6 millimeters, butcan range from about 3 millimeters to about 12 millimeters. Thisincludes, for example, 3.5, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5,10, 10.5, 11, 11.5, or 11.9 millimeters. Diameter D2 may be less than 3millimeters or greater than 12 millimeters.

In a specific implementation, diameter D3 is about 5.5 millimeters, butcan range from about 2 millimeters to about 10 millimeters. Thisincludes, for example, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8,8.5, 9, 9.5, or 9.9 millimeters. Diameter D3 may be less than 2.5millimeters or greater than 10 millimeters.

In a specific implementation, length L10 of the block is about 5millimeters, but can range from about 2 millimeters to about 10millimeters. This includes, for example, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6,6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 9.9 millimeters. Length L10 may be lessthan 2 millimeters or greater than 10 millimeters.

The block has a surface or face 620 which faces the bone to be measured.In a specific implementation, an area of the face is about 23.8 squaremillimeters. An area of the face may be about 24 square millimeters orless, but can range from about 5 square millimeters to about 80 squaremillimeters. This includes, for example, 10, 15, 20, 25, 30, 35, 40, 45,50, 55, 60, 65, 70, 75, or 79.9 square millimeters. The area may be lessthan 5 square millimeters or greater than 80 square millimeters. Sensorheads having small faces (i.e., small surface areas) may be used whereonly a small portion of the surface of the bone is exposed or available.Small sensor heads are desirable because they allow for smallerincisions in the soft tissue to reach the underlying bone as compared tolarge sensor heads.

It should be appreciated that these dimensions and other dimensionsdiscussed in this application may vary widely depending upon theapplication, the dimensions of the bone to be measured, or both.Generally, it will be desirable to select a sensor head with a sensorsurface that can make good contact (e.g., full contact) with the surfaceof the bone to be measured. This helps to ensure that light from thesensor head is directed into the bone and that reflected light from thebone (not ambient light) is received at the sensor head.

In a specific implementation, the face of the block has a dull finish.This can help to ensure that that more of the light which is transmittedinto the bone is received back at the detectors, instead of beingreflected off the face. The face of the block may be processed (e.g.,polishing, sanding, bluing, anodizing, or oxidizing) to make the facemore dull than the original starting material. In a specificimplementation, the face is processed with a final polish of a 5 microngrit abrasive for a dull finish on the face. The abrasive may be a pieceof paper (e.g., sandpaper), a polishing compound, or a stone. The facemay be colored (e.g., black flat color), finished (e.g., matte finish),textured (e.g., bead-blasted finish), or combinations of these, toreduce reflectivity.

It should be appreciated that the block, elongated member or both maynot necessarily have a cylindrical shape. In various implementations,the block, elongated member or both have a rectangular shape anddimensions are with respect to widths and lengths. The block, elongatedmember or both have a triangular shape and dimensions are with respectto bases and altitudes or heights. The block, elongated member or bothhave an elliptical or oval shape and dimensions are with respect to amajor axis (or transverse diameter) and a minor axis (or conjugatediameter). It should be appreciated that the block, elongated member orboth can have any cross-sectional shape.

This specific implementation of the bone oximeter probe may be referredto as a probe with a forward-looking sensor array. In this specificimplementation, the sensor head (or sensor head surface) is positionedwith respect to the elongated member such that the optical fibers extendthrough the probe or through the elongated member and to the sensor headsurface without changing direction. The optical fibers are straight(i.e., not bent). In other words, the sensor head surface is positionedwith respect to the elongated member such that an axis passing throughthe elongated member passes through the sensor head surface. Whenholding or pointing the elongated member towards the bone to bemeasured, the sensor head surface will be facing the bone. Thus, thedoctor will not have to reorient the probe to make the sensor head facethe bone which can be difficult when the sensor head is within anincision. In other implementations, a bone oximeter probe may instead oradditionally have a side-looking sensor array such as shown in FIGS.15-17 and discussed below.

FIGS. 7-12 show various specific implementations of arrangements forsensor structures or openings of a probe. Any of these implementationsmay be used in conjunction with any of the implementations discussed inthis application. The sensor structures can be either source structuresor detector structures. Although specific numbers of sensor structuresare shown, the arrangements can be expanded or reduced to have moresensor structures per column, more sensor structures per row, lesssensor structures per column, less sensor structures per row, orcombinations of these.

FIG. 7 shows a front view of a probe 705. This probe has four structures710 a-d. Structure 710 a is in a first column. Structures 710 b-c are ina second column. Structure 710 d is in a third column. Each column hasthree rows. Structure 710 b is in a first row. Structures 710 a and 710d are in a second row. Structure 710 c is in a third row. In otherimplementations, there can be any number of structures arranged in anynumber of desired rows and columns (e.g., one by two, one by three, oneby four, two by two, or two by four).

This application describes the arrangement of sensors as an array ofrows and columns, but as one of skill in the art will recognize, theentire array can be rotated ninety degrees, so that rows become columnsand columns become rows. A row may have a different number of structuresthan another row. A column may have a different number of structuresthan another column. A row or column may be composed entirely of onetype of structure, either source or detector. A row or column may becomposed of both source and detector.

In a first arrangement, structures 710 a-b are source structures (i.e.,first and second source structures, respectively) and structures 710 c-dare detector structures (i.e., first and second detector structures). Inother implementations, any of the structures can be assigned as sourcesor detectors as desired.

The intensity of light emitted by the source structures may be the sameor the intensity may vary. For example, in a specific implementation ofthe first arrangement, first source structure 710 a emits light at anintensity that is the same as second source structure 710 b. In anotherimplementation, first source structure 710 a emits light at an intensitythat is different from second source structure 710 b. For example, theintensity of light emitted by second source structure 710 b may begreater than the intensity of light emitted by first source structure710 a. This can help to compensate for the attenuation of light if adistance between second source structure 710 b and first detectorstructure 710 c is greater than a distance between first sourcestructure 710 a and second detector structure 710 d.

In FIG. 7, the structures shown are circular. However, in otherimplementations, the structures can have any shape, such as square,rectangle, hexagon, octagon, ellipse, any polygon shape, or anyquadrilateral shape. In a specific implementation, each structure hasthe same cross-sectional area (e.g., same diameter). In anotherimplementation, the cross-sectional area of one or more structures maybe different from other structures. There can be any combination ofdifferently sized structures.

In this specific implementation, each structure has a diameter of about1 millimeter. More specifically, each structure includes an opticalfiber bundle having a diameter of about 1 millimeter. The optical fiberbundle includes borosilicate glass fibers having a diameter of 33microns or micrometers. The diameter of a structure or optical fiberbundle can range from about 0.5 millimeters to about 2 millimeters. Thisincludes, for example, 0.6, 0.7, 0.8, 0.9, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6,1.7, 1.8, or 1.9 millimeters. The diameter may be less than 0.5millimeters or greater than 2 millimeters. Smaller diameter structuresmay be desirable for smaller bones. This helps to ensure that gapsbetween the structure and the surface of the bone is minimized so thatlight from a source structure does not escape through a gap and ambientlight does not enter through the gap and be detected by the detectorstructure.

Using optical fiber instead of photodetectors and emitters (e.g., lightemitting diodes) can reduce the cost of the probe because, typically,optical fiber is less expensive than photodetectors and diodes. Further,the probe face can be made to have a small surface area which can bedesirable because such a probe face will not need a large surface areaof bone to be exposed.

In other implementations, wires or cables may be connected to thestructures. One or more of the structures may include a photodiode orother emitter device, a photodetector or other detector device, or fiberoptic cable, in any combination.

Distances between columns and rows can be the same or different.Distance can be measured from a reference line for each column and rowwhere the reference line passes through a reference point of thestructure. For example, this reference point may be the centers of thestructures.

Thus, in FIG. 7, a first reference line 720, parallel to an x-axis 725a, passes through a reference point of second source structure 710 b. Asecond reference line 730, parallel to the x-axis, passes throughreference points of first source structure 710 a and second detectorstructure 710 d. A third reference line 735, parallel to the x-axis,passes through a reference point of first detector structure 710 c. Afourth reference line 740, parallel to a y-axis 725 b, passes throughfirst source structure 710 a. A fifth reference line 745, parallel tothe y-axis, passes through second source structure 710 b and firstdetector structure 710 c. A sixth reference line 750 parallel to they-axis passes through second detector structure 710 d.

In a specific implementation, the sensor structures are asymmetricallyarranged. A distance D20 between the first and second reference lines isdifferent from a distance D25 between the second and third referencelines. Distance D20 may be about 1.5 millimeters, but can range fromabout 0.5 millimeters to about 3 millimeters. This includes, forexample, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8,1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, or 2.9 millimeters.Distance D20 may be less than 0.5 millimeters or greater than 3millimeters.

Distance D25 may be about 2 millimeters, but can range from about 1millimeter to about 4 millimeters. This includes, for example, 1.1, 1.2,1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7,2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, or 3.9 millimeters.Distance D25 may be less than 1 millimeter or greater than 4millimeters.

In another implementation, the sensor structures are symmetricallyarranged. Distances D20 and D25 are the same. For example, distances D20and D25 may be about 1.5 millimeters. A sensor head having a symmetricalarrangement of sensor structures can accommodate a desire to have asmall sensor head (i.e., a sensor head having a small surface area) anda desire to have a large source and detector separation. When using asmall sensor head, there is typically less bone that will be exposed ascompared to using a large sensor head. A large source and detectorseparation allows measurements to be made deeper into the bone ascompared to a small source and detector separation. To achieve a largesource and detector separation with a sensor head having a symmetricalshape or surface (e.g., circle), the source structures can be placedclose to an edge of the sensor head surface while the detectorstructures are placed to close to opposite or diametric edges of thesensor head surface. In this specific implementation, this creates asymmetrical arrangement of sensor structures when the structures are soarranged.

A distance D30 between the fourth and fifth reference lines is the sameas a distance D35 between the fifth and sixth reference lines. DistancesD30 and D35 may be about 1.5 millimeters, but can range from about 0.5millimeters to about 3 millimeters. This includes, for example, 0.6,0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1,2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, or 2.9 millimeters. Distances D30 andD35 may be less than 0.5 millimeters or greater than 3 millimeters. Inanother implementation, distance D30 may be different from distance D35.

The sensor arrangement shown in FIG. 7 may be referred to as a kite ordeltoid array of sensors. A deltoid is a quadrilateral with two disjointpairs of congruent sides. In this specific implementation, structures710 a-d form the vertices of a deltoid. A first side of the deltoid isbetween first and second source structures 710 a-b. A second side of thedeltoid is between second source structure 710 b and second detectorstructure 710 d. A third side of the deltoid is between first and seconddetector structures 710 c-d. A fourth side of the deltoid is betweenfirst source structure 710 a and first detector structure 710 c.

Lengths of the first and second sides of the deltoid are the same.Lengths of the third and fourth sides of the deltoid are the same. Alength of the first or second side is less then a length of the third orfourth side. The first side is not parallel with the second, third, orfourth sides. The second side is not parallel with the third and fourthsides. The third side is not parallel with the fourth side. A firstdiagonal is from second source structure 710 b to first detectorstructure 710 c. A second diagonal is from first source structure 710 ato second detector structure 710 d. The first diagonal bisects thesecond diagonal at right angles.

In another implementation, the sensors are arranged in a symmetricaldiamond or square array. In other words, structures 710 a-d form thevertices of a square. A first side of the square is between first andsecond source structures 710 a-b. A second side of the square is betweensecond source structure 710 b and second detector structure 710 d. Athird side of the square is between first and second detector structures710 c-d. A fourth side of the square is between first source structure710 a and first detector structure 710 c. The first side isperpendicular to the second and fourth sides. The second sideperpendicular to the first and third sides. The third side perpendicularwith the second and fourth sides. The first side is parallel with thethird side. The second side is parallel with the fourth side.

Lengths of the first, second, third, and fourth sides of the square arethe same. In this specific implementation, distances D20, D25, D30, andD35 are equal. For example, distances D20, D25, D30, and D35 may beabout 1.5 millimeters. Structures 710 a-d may be arranged to form thevertices of any shape. Some examples of shapes include a polygon, convexpolygon, non-convex polygon, equiangular polygon, cyclic, equilateral,isotoxal, regular, rectilinear, quadrilateral, convex quadrilateral,concave quadrilateral, rectangle, parallelogram, rhombus, rhomboid,kite, deltoid, tangential quadrilateral, and trapezium.

In a specific implementation, a first distance extends between the firstsource structure and the first detector structure without touchinganother source or detector structure. A second distance extends betweenthe second source structure and the second detector structure withouttouching another source or detector structure. The first distance isdifferent from the second distance.

FIG. 8 shows a front view of a specific implementation of a probe 805.In this probe, structures 810 a-d are arranged symmetrically in one rowand four columns. Structures 810 a-b are source structures (i.e., firstand second source structures, respectively) and structures 810 c-d aredetector structures (i.e., first and second detector structures,respectively). This arrangement of structures may be referred to as alinear arrangement. This sensor head may be referred to as a lineartwo-source two-detector sensor (i.e., linear 2s2d sensor). Distancesbetween adjacent structures may be equal or different.

For example, a first reference line 815, parallel to an x-axis 825 a,passes through reference points of structures 810 a-d. A secondreference line 830, parallel to a y-axis 825 b, passes through areference point of first source structure 810 a. A third reference line835, parallel the y-axis, passes through a reference point of secondsource structure 810 b. A fourth reference line 840, parallel to they-axis, passes through a reference point of first detector structure 810c. A fifth reference line 845, parallel to the y-axis, passes through areference point of second detector structure 810 d.

A first distance D40 is between the second and third reference lines. Asecond distance D45 is between the third and fourth reference lines. Athird distance D50 is between the fourth and fifth reference lines.

In a specific implementation, the first, second, and third distances arethe same. The first, second, and third distances may be about 1.5millimeters. In another implementation, at least one distance isdifferent from another distance. For example, the first distance may bedifferent from the second and third distances. The second distance maybe different from the third distance.

In a specific implementation, the first reference line is coincidentwith a diameter or diagonal of the sensor head face. An axis passingthrough the elongated member that is connected to the sensor head isperpendicular to the first reference line. In another implementation,sensor structures are not aligned with the diameter of the sensor headface. The sensor structures may be aligned with a chord of the sensorhead face.

Selection of a sensor head having a specific arrangement of sensors maydepend on the type of bone to be measured. For example, the linear arrayof sensors (FIG. 8) may be more desirable for bones that are small andlong as compared to bones that are wide and flat because the lineararray of sensors can be aligned with the axis of the bone. The sensorhead of FIG. 8 may make better contact with the small and long bone ascompared to the sensor head of FIG. 7. Conversely, the rectangular ordeltoid array of sensors (FIG. 7) may be more desirable for bones thatare wide and flat as compared to bones that are small and long.

The length and width of the source and detector array may be customizedfor certain types of bone to better match the anatomy. In a specificimplementation, a probe includes pluggable sensor heads. A user canunplug a sensor head of a first type (e.g., linear sensor array) from aprobe and plug a sensor head of a second type (e.g., rectangular sensorarray) into the probe.

FIG. 9 shows a front view of a specific implementation of a probe 905.In this probe, structures 910 a-d are arranged asymmetrically in tworows and four columns. Structures 910 a-b are source structures (i.e.,first and second source structures, respectively) and structures 910 c-dare detector structures (i.e., first and second detector structures,respectively). First and second source structures and the first detectorstructure are aligned linearly. The second detector structure is offsetfrom the rest of the sensor structures and is not aligned linearly withthe first and second source structures and the first detector structure.

In other words, a first row includes first and second source structuresand the first detector structure. A second row includes the seconddetector structure. First, second, third, and fourth columns include thefirst source structure, second source structure, first detectorstructure, and second detector structure, respectively.

A first reference line, parallel to an x-axis, passes through the firstand second source and first detector structure. A second reference line,parallel to the x-axis, passes through the second detector structure.The first and second reference lines are not coincident. In other words,second reference line is offset from the first reference line. Thesecond reference line may be offset from the first reference line by anydistance (e.g., 0.5, 1, 1.5, 2, 2.5, or 3 millimeters).

A third reference line, parallel to a y-axis, passes through the firstsource structure. A fourth reference line, parallel to the y-axis,passes through the second source structure. A fifth reference line,parallel to the y-axis passes through the first detector structure. Asixth reference line, parallel to the y-axis, passes through the seconddetector structure.

A first distance is between the third and fourth reference lines. Asecond distance is between the fourth and fifth reference lines. A thirddistance is between the fifth and six reference lines.

In a specific implementation, the first, second, and third distances arethe same. In another implementation, at least one distance is differentfrom another distance. For example, the first distance may be differentfrom the second and third distances. The second distance may bedifferent from the third distance.

FIG. 10 shows a front view of a specific implementation of a probe 1005.In this probe, structures 1010 a-d are arranged asymmetrically in tworows and two columns. Structures 1010 a-b are source structures (i.e.,first and second source structures) and structures 1010 c-d are detectorstructures (i.e., first and second detector structures). First andsecond source structures and the first detector structure areequidistance from the center of the probe face. The second detectorstructure is farther away from the center of the probe face compared tothe other three structures. Also, a line drawn through the first andsecond source structures is not parallel to a line drawn through thefirst and second detector structures.

In other words, a first row includes first and second source structures.A second row includes first and second detector structures. However, thesecond detector structure is offset from the first detector structure ina vertical direction or in a direction parallel to the y-axis.

A first column includes the first source and first detector structures.A second column includes the second source and second detectorstructures. However, the second detector structure is offset from thesecond source structure in a horizontal direction or in a directionparallel to the x-axis. A structure may be offset with respect to bothhorizontal and vertical directions, offset with respect to thehorizontal direction only, or offset with respect to the verticaldirection only.

FIG. 11 shows a front view of a specific implementation of a probe 1105.This probe has one source structure 1110 and one detector structure1115. This sensor head may be referred to as a linear one-sourceone-detector sensor (e.g., a linear 1s1d sensor). A distance between acenter of the probe face and the source structure may be equal to ordifferent from a distance between the center of the probe face and thedetector structure.

FIG. 12 shows a front view of a specific implementation of a probe 1205.This probe has one source structure 1210 and two detector structures1215 a-b (i.e., first and second detector structures). A distancebetween the source structure and the first detector structure may beequal to or different from a distance between the source structure andthe second detector structure.

The source structure and first and second detector structures may bearranged to form the vertices of a triangle. A first side of thetriangle is between the source structure and first detector structure. Asecond side of the triangle is between the first and second detectorstructures. A third side of the triangle is between the source structureand the second detector structure.

In a specific implementation, the triangle is a right triangle such thatthe third side forms the hypotenuse and the first and second sides areperpendicular to each other. A length of the third side is greater thanlengths of the first and second sides. The structures may be arranged toform other types of triangles such as an isosceles, scalene,equilateral, oblique, acute, or obtuse triangle.

Generally, a source structure and a detector structure are separated bya larger distance when optical measurements from a deeper volume of boneare desired. Thus, a sensor unit with a larger distance between a sourcestructure and a detector structure can generally measure opticalparameters deeper into the tissue. In other words, the distance betweenthe source and detector (i.e., “source-detector separation”) canindicate the approximate depth below the surface of the bone at which ameasurement will be made.

More specifically, if the source-detector separation of the sensor is“S” then the region of bone below the surface of the bone (or below thesensor) that will be measured will have a cubic volume of S×S×S (S by Sby S). For example, if a sensor has a source-detector separation that is5 millimeters, the region measured below the surface of the bone has acubic volume of about 5 millimeters by 5 millimeters by 5 millimeters.As another example, if a sensor has a source-detector separation that is2.2 millimeters, the region measured below the surface of the bone has acubic volume of about 2.2 millimeters by 2.2 millimeters by 2.2millimeters. Thus, typically, the source-detector separation will not begreater than a thickness of the bone; otherwise, the sensor may make ameasurement of a region outside of the bone.

For example, the human femur bone has a cortical wall that varies inthickness from about 2 millimeters to about 10 millimeters. Thus, tomeasure the bone oxygenation of a cortical wall that is about 2millimeters thick, it may be desirable to use a sensor head having asource-detector separation of less than 2 millimeters. To measure thebone oxygenation of a cortical wall that is about 10 millimeters thick,it may be desirable to use a sensor head having a greatersource-detector separation so that a deeper region of the cortical wallis measured. In a specific implementation, a measurement depth of a boneoximeter probe is about 5 to about 10 millimeters.

In a specific implementation, a distance between a source and detectorstructure is about 3.5 millimeters or less, but can range from about 1millimeter to about 10 millimeters. This includes, for example, 1.5, 2,2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 9.9millimeters. The distance may be less than 1 millimeter or greater than10 millimeters.

In some implementations, it is desirable to have a large source-detectorseparation and a small sensor head face (e.g., small surface area). Thelarge source-detector separation allows thick bones to be measured andthe small sensor face allows a relatively small surface area of bone tobe exposed for the sensor head. In these implementations, it may bedesirable to position source and detector structures near the edges ofthe sensor face so that there can be a large source and detectorseparation.

Thus, in a specific implementation, distances between sensor structuresand an edge of the sensor head defining the face of the sensor head areabout 1.2 millimeters. The distance may be about 1.5 millimeters orless, but can range from about 0.2 to about 5 millimeters. Thisincludes, for example, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.3,1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8,2.9, 3, 3.5, 4, 4.5, or 4.9 millimeters. The distances may be less than0.2 millimeters or greater than 5 millimeters.

It may be desirable to position a source and a detector such that alongest line across the face of the sensor head has the source at oneend of the line and the detector at an opposite end of the line. Thisallows for a large measurement depth for a given sensor. The longestline may be a diameter if the sensor face has the shape of a circle. Thelongest line may be diagonal if the sensor face has the shape of asquare.

While FIGS. 7-12 show embodiments with two, three, or four sensoropenings in the sensor unit, any suitable number of sensor openings canbe present in the sensor unit. For example, there may be one, two,three, four, five, six, seven, or eight or more sensor openings. Any oneor more sensor openings can be source structures, and any one or moresensor openings can be detector structures. A number of sourcestructures can be equal to a number of detector structures in the sensorunit, or they can be different.

In a specific implementation, a sensor head has an asymmetricarrangement of two source structures and four detector structures. Thissensor head may be referred to as an asymmetric 2s4d sensor. In thisspecific implementation, the four detector structures are arranged on afirst line. The first source structure is below the first detectorstructure of the four detector structures. The second source structureis below the last detector structure of the four detector structures. Adistance between the first source structure and first detector structureis different from a distance between the second source structure andlast detector structure. The first source structure may be directlybelow the first detector structure. That is, a second line passingthrough the first source structure and first detector structure isperpendicular to the first line. The second source structure may bedirectly below the last detector structure. That is, a third linepassing through the second source structure and last detector structuremay be perpendicular to the first line. In other implementations, thefirst source structure is not directly below the first detectorstructure. That is, the second line may be oblique to the first line.The second source structure is not directly below the last detectorstructure. That is, the third line may be oblique to the first line.

In implementations discussed so far in this application, each opening ofthe sensor head has a single fiber optic cable associated with it.However, in further implementations of the invention, each opening ofthe sensor head may have multiple fibers optic cables—two ormore—associated with it. Or, each opening of the sensor head may havemultiple light paths or light channels associated with it.

These light paths can be used simultaneously for transmitting to bone orreceiving light from bone. Within a single opening, there may be twosource structures, two detector structures, or one source and onedetector structure. And for a single sensor head, there may be two ormore such openings with multiple light channels.

In other words, in a specific implementation, a single opening on thesurface of the sensor head holds a single fiber optic cable that hasboth source and detector light channels. For example, the single fiberoptic cable may be a concentric core fiber having an inner core lightchannel which is surrounded by an outer core light channel. In thisspecific implementation, one of the inner core light channel or outercore light channel is a source channel and another of the inner corelight channel or outer core light channel is a detector channel.

Sensor head openings having multiple light channels are furtherdiscussed in U.S. patent application Ser. No. 12/194,508, filed Aug. 19,2008, which is incorporated by reference.

There are various other implementations of sensor opening patterns whichcan be incorporated into a sensor unit. Some of these implementationsare discussed in U.S. Pat. No. 7,355,688, issued Apr. 8, 2008, U.S.patent application Ser. No. 12/126,860, filed May 24, 2008, U.S. patentapplication Ser. No. 12/178,359, filed Jul. 23, 2008, and U.S. patentapplication Ser. No. 12/410,007, filed Mar. 24, 2009. These patent andpatent applications are assigned to the same assignee as this patentapplication and are incorporated by reference.

Although FIGS. 7-12 show embodiments of the invention where opticalfibers are inside the elongated member, optical fibers may be locatedelsewhere. FIGS. 13-14 show embodiments in accordance with the presentinvention where optical fibers are not located inside a lumen orpassageway of the elongated member, but are coupled to an outer surfaceof the elongated member.

FIG. 13 shows a bone oximeter probe 1305 that includes an elongatedmember 1310 and a sensor probe 1315 which surrounds the elongatedmember. The sensor probe includes four optical fibers 1320 in a sheathmaterial 1325 which surrounds and holds the optical fibers in theirpositions. The sheath material may be any suitable biocompatiblematerial such as silicone or polyurethane.

FIG. 14 shows another bone oximeter probe 1405 with an elongated member1410 and a sensor probe 1415 which is axially aligned with and attachedto an outer surface of the elongated member. The sensor probe has twooptical fibers 1420 which are surrounded by a sheath material 1425.

In a specific implementation, the elongated member is a solid rod thatdoes not have a passageway or lumen. That is, the elongated member isnot hollow. The elongated member as shown, for example, in FIGS. 13-14,may be a solid bar, shaft, stick, or dowel. The elongated member mayhave a channel or groove extending lengthwise along its outer surface tohold a fiber optic cable. In this specific implementation, the opticalfibers are outside the elongated member or attached to an outer surfaceof the elongated member rather than being inside the elongated member.The elongated member may be a solid rod that has channels or holesextending between opposite ends of the elongated member. Each channelmay hold a single conductor or optical fiber cable.

In another specific implementation, the elongated member is hollow orhas a passageway or lumen and at least some optical fibers are attachedto an outer surface of the elongated member. In this specificimplementation, the passageway allows instruments (e.g., surgical tools)to be passed through the passageway. Some examples of instrumentsinclude a camera, dissector, grasper, forceps, scissor, needle holder,fan retractor, cautery tools, puncture needle, and K-wire.

FIG. 15 shows another implementation of a bone oximeter probe 1505 wherea scanning surface with sensor openings is located on a sidewall of anelongated member 1510 at or near its distal end region. FIG. 16 shows alongitudinal cross section of a tip region 1515 of the probe shown inFIG. 15.

Referring now to FIG. 16, bone oximeter probe 1505 includes a sensorhead 1610 which includes distal ends of optical fibers 1615. A sensorunit or sensor head refers to a portion of a device (typically locatedat a distal end region of the device) which has sensor openings coupledwith optical fibers and provides a scanning surface or surfaces to makeoptical measurements.

In the implementation shown in FIGS. 15-16, four sensor openings 1620 ofthe bone oximeter probe are located on a sidewall of a distal end regionof the elongated member, rather than at the open end of the elongatedmember at its tip as shown in FIGS. 5-6. The bone oximeter probe shownin FIGS. 15-16 may be referred to as a device with a side-looking sensorarray, whereas the probe device shown in FIGS. 5-6 may be referred to asa device with a forward-looking sensor array. A bone oximeter probe witha side-looking sensor array can make measurements of bone where the boneis located adjacent to the sidewall of the elongated member, whereas abone oximeter probe with a forward-looking sensor array can makemeasurements where the bone is located in front of the tip of the probe.

As shown in FIG. 16, the distal ends of the optical fibers are coupledto the sensor openings on the side wall of the elongated member. In thisimplementation, sensor unit 1610 includes optical fibers 1625 a-d whichare threaded and inserted into four channels which are located on a sidewall of elongated member 1510 near its tip. As shown in FIG. 16, thedistal ends of the optical fibers are flushed with the outer surface ofthe elongated member sidewall to provide a side-looking sensor array. Inanother implementation, the distal ends of the optical fibers arerecessed below a surface of the sidewall or project beyond the surfaceof the sidewall.

The optical fibers may be adhesively attached inside the elongatedmember to prevent them from moving around. A block (e.g., cylindricalblock) 1630 may be used to block the lumen of the elongated member atits tip to prevent tissue debris from entering into the bone oximeterprobe during a surgical procedure.

In the implementation shown in FIGS. 15-16, the sensor openings arearranged in a linear array. In one embodiment, the distal ends ofoptical fibers 1625 a-b may be source structures (i.e., first and secondsource structures, respectively) which transmit light from a lightsource into bone, and the distal ends of optical fibers 1625 c-d may bedetector structures (i.e., first and second detector structures,respectively) which detect or collect light reflected from the bone andtransmit the reflected light to a photodetector.

In other implementations, sensor openings of the side-looking sensorarray may be arranged in the sensor patterns shown in FIGS. 7 and 9-12and discussed above. There may be more than four sensor openings or lessthan four sensor openings. For instance, a bone oximeter probe may havemultiple sets (e.g., three, four, five, six, or more) of sensor openingsin a linear array all the way around the sidewall at a distal end regionof the elongated member.

In various specific implementations, a probe with a side-looking sensorarray includes a tube having a distal end and a proximal end, oppositethe distal end, a set of sensor openings, and a cable extending from theproximal end of the tube. A sidewall of the tube is between the distaland proximal ends. The distal end may be closed or sealed. For example,a plug or block may be inserted into the distal end. The set of sensoropenings are on the sidewall tube. The set of sensor openings are closeror nearer to the distal end than the proximal end.

The set of sensor openings may be arranged linearly with respect to anaxis passing through the tube. That is, a line passing through the setof sensor openings is parallel to the axis passing through the tube. Inthis specific implementation, a first sensor opening of the set ofsensor openings is nearer to the distal end than a second sensor openingof the set of sensor openings. A length of a first optical fiberconnected to the first sensor opening is greater than a length of asecond optical fiber connected to the second sensor opening.

The set of sensor openings may be arranged along a circumference of orradially about the tube. In this specific implementation, there arefirst and second sensor openings of the set of sensor openings. A firstdistance is from the distal end to the first sensor opening. A seconddistance is from the distal end to the second sensor opening. The firstdistance is equal to the second distance. A length of a first opticalfiber connected to the first sensor opening is equal to a length of asecond optical fiber connected to the second sensor opening.

The set of sensor openings may be arranged along a helix of the tube. Inthis specific implementation, a first distance is from the distal end ofthe tube to the first sensor opening. A second distance is from thedistal end of the tube to the second sensor opening. The second distanceis greater than the first distance. A length of a first optical fiberconnected to the first sensor opening is greater than a length of asecond optical fiber connected to the second sensor opening.

In other various specific implementations, a probe with aforward-looking sensor array includes a tube having a distal end and aproximal end, opposite the distal end, a set of sensor openings, and acable extending from the proximal end of the tube. A sidewall of thetube is between the distal and proximal ends. The sidewall is closed anddoes not have any openings. Rather, it is the distal end that includes aset of openings. Each opening holds a fiber optic cable. The fiber opticcables are straight. That is, the fiber optic cables extend from theproximal end to the distal end without changing direction. For example,there are no bends or angles. Lengths of the fiber optic cables are thesame. The fiber optic cables within the tube run in a direction parallelto an axis passing through the tube.

Light directed into the bone via a first fiber optic cable travels in afirst direction from the proximal end towards the distal end and exits afirst opening in the first direction. Light reflected from the boneenters a second opening in a second direction. The reflected lighttravels from the distal end towards the proximal end in the seconddirection and through a second fiber optic cable. The second directionis opposite the first direction.

FIG. 17 shows another implementation of a bone oximeter probe 1705having a sensor head 1710 which includes distal end portions of two setsof optical fibers—a first set 1715 which forms a forward-looking sensorarray and a second set 1720 which forms a side-looking sensor array.

The distal end regions of the first set of optical fibers are alignedalong the longitudinal axis of the elongated member, and are insertedinto channels of a block 1725. The block may be attached to an innerwall of the elongated member by an adhesive. The distal end portions ofthe second set of optical fibers are inserted into channels on thesidewall of the elongated member, and the distal ends of the opticalfiber are flushed with the outer surface of the elongated membersidewall. If desired, an adhesive may be used to firmly attach thesecond set of optical fibers inside the lumen of the elongated member.In this implementation, since the bone oximeter probe includes both theforward-looking sensor array and the side-looking sensor array, theprobe can make measurements of bone where a bone is in front of the tipof the probe as well where a bone is on a side of the probe.

In a specific implementation, the optical fibers forming theforward-looking sensor array are attached to a first channel (e.g., areceptacle) of the system unit, and the optical fibers forming theside-looking sensor array are attached a second, independent channel(e.g., receptacle) of the system unit. The optical fibers forming theforward looking sensor array and the optical fibers forming theside-looking sensor array may be directly attached to the first channeland second channel, respectively, of the system unit. Alternatively, theproximal end portions of the optical fibers forming the forward-lookingsensor array can be coupled to a connector, which then connects theoptical fibers to the first channel of the system unit. Also, theproximal end portions of the optical fibers forming the side lookingsensor array can be coupled to another connector, which then connectsthe optical fibers to the second channel of the system unit.

By using separate channels in the system unit, optical signals to andfrom the fibers of the forward-looking sensor array can be controlledindependently from optical signals to and from the fibers of theside-looking sensor array. For example, the optical signals to and fromthe sensors connected to the first channel will not interfere with thoseon the second channel, and vice versa. Any signals transferred over thefirst channel will appear only at the sensors attached to the firstchannel or at the first channel input of the system unit. Any signalstransferred over the second channel will appear only at the sensorsattached to the second channel or at the first channel input of thesystem.

In another implementation, the proximal ends of both sets of opticalfibers (i.e., forward-looking sensor and side-looking sensor) can beattached to a single connector, which can then be connected to a singlechannel of the system unit. It may be desirable to use a singleconnector for all of the optical fibers and attach the connector to asingle channel of the system unit to reduce cost, if the total number ofoptical fibers included in a bone oximeter probe is not too large (e.g.,eight or less).

FIG. 18 shows a longitudinal cross section of a tip of a bone oximeterprobe 1805. This probe includes a sensor head 1820 that is deformable orhas a deformable surface. This specific implementation of the sensorhead includes a soft deformable block 1830 and a solid un-deformable (ornondeformable or nondeforming) block 1832 (to hold the fibers separatedas shown). A distance D65 indicates the distance or length of a portion1825 of the deformable block that is outside the elongated member orprotrudes out from the distal end of the elongated member.

The sensor head includes a set of channels 1835 for a set of fiber opticcables 1840. In a specific implementation, a channel is continuousthrough the nondeformable block and the deformable block. In otherwords, there is a single channel extending through the nondeformableblock and the deformable block.

In another implementation, the channel is discontinuous. For example, agap or space may be between the nondeformable block and the deformableblock. In this specific implementation, the nondeformable block includesa first channel and the deformable block includes a second channel. In aspecific implementation, an end of the first channel faces an end of thesecond channel so that a single fiber optic cable can pass through thefirst channel, span the gap between the nondeformable block and thedeformable block, and continue through the second channel. In anotherimplementation, an end of the first channel faces an end of the secondchannel. The first channel holds a first fiber optic cable and thesecond channel holds a second fiber optic cable. Light passing throughthe first fiber optic cable in the first channel can continue throughinto the second fiber optic cable in the second channel.

In a specific implementation, the fibers reach the very end of thedeformable block 1830. That is, the fibers extend to a surface 1841 ofthe deformable block. Surface 1841 may be referred to as a bone facingsurface or bone contacting surface. Ends of the fibers are flush withsurface 1841. In other words, surface 1841 lies in a plane and ends ofthe fibers lie or are on the plane (i.e., same plane).

In other implementations, the fibers terminate before reaching thesurface or the fibers extend past the surface. An implementation mayhave one or more fibers which are flush with the surface, one or morefibers which terminate before reaching the surface, one or more fiberswhich extend past the surface, or combinations of these.

An adhesive, such as epoxy, may be used to connect or secure thedeformable block and nondeformable block together. The deformable blockmay be referred to as a pad, cushion, pillow, adapting pad, orconforming pad. The deformable block may be made of any material that isflexible, springy, elastic, compliant, or pliable. For example, thedeformable block may be made of foam (e.g., polyethylene foam), silicon,rubber, neoprene, or a gel. The deformable block can be of any length.For example, the length of the deformable block may range from about 3millimeters to about 10 millimeters. This includes, for example, 3.5, 4,4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 9.9 millimeters. Thelength may be less than 3 millimeters or greater than 10 millimeters.

The nondeformable block may be made of material that is different from amaterial of the deformable block, such as a rigid material. Thenondeformable block may be made of materials similar to that of block610 (FIG. 6), such as aluminum (e.g., 6061 aluminum).

In a specific implementation, a length of the nondeformable block isgreater than a length of the deformable block. In other implementations,the length of the nondeformable block is less than a length of thedeformable block. The length of the nondeformable block may be equal toa length of the deformable block.

In FIG. 18 a portion of the deformable block is inside the elongatedmember (i.e., inside a passageway of the elongated member). In otherimplementations, the deformable block is completely outside of theelongated member. For example, in a specific implementation, thenondeformable block extends to the edge of the elongated member, isflush with the edge, or extends past the edge. The deformable block isattached to the nondeformable block and is outside the elongated member.

In a specific implementation, surface 1841 of the deformable block isflat or planar. In other implementations the surface is not flat. Forexample, the surface can be curved convex or concave as shown in FIGS.21-24 in order to match or conform to the surface of the bone to bemeasured.

FIG. 19 shows a longitudinal cross section of the bone oximeter probe ofFIG. 18 being placed against a bone 1901. The surface of this bone isnot flat. Rather, the surface of this bone includes curves and otheranatomical features. Deformable block 1830 can compress or deform aroundthese features as shown in FIG. 19 so that there is good contact betweenthe sensor head and the surface of the bone.

The deformable block allows accurate bone measurements to be made onbone surfaces that include various anatomical features (e.g., ridges,bumps, valleys, and protrusions) because the deformable block helps toseal the sensor head against the surface of the bone. Thus, light fromthe source fibers is directed into the bone rather than being scatteredoutside the bone. Similarly, the detector fibers can detect lightreflected from the bone rather than ambient light.

In other words, when the sensor head is placed against a bone, thedeformable block can deform and adapt to the various surface features orcontours of the bone. This helps to ensure that more of the light whichis transmitted out of the sensor head is transmitted into the bone andthat more of the light which is then reflected from the bone is receivedat the sensor head.

Some specific examples of anatomical features of a bone include thearticular process, articulation, canal, condyle, crest, eminence,epicondyle, facet, foramen, fossa, fovea, labyrinth, line, malleolus,meatus, process, ramus, sinus, spine, suture, trochanter, tubercle, andtuberosity.

In a specific implementation, the optical fibers are designed to flex,bend, or slide within the channels, passageway of the elongated member,or both as the deformable block is compressed. For example, the opticalfibers may be threaded through the channels, but not fixedly securedwithin the channels so that the optical fibers can slide. Alternatively,the optical fibers may be partially secured within the channels such aswith an adhesive at a proximal end of the channel and no adhesive at adistal end of the channel.

Referring now to FIG. 18, distance D65 ranges from about 1 millimeter toabout 2 millimeters. This includes, for example, 1.1, 1.2, 1.3, 1.4,1.5, 1.6, 1.7, 1.8, or 1.9 millimeters. Distance D65 may be less than 1millimeter or greater than 2 millimeters. In other implementations,distance D65 ranges from about 0.5 millimeters to about 5 millimeters.Typically, the thicker the deformable block (i.e., a greater distanceD65), the more that the block can compress. Thus, thicker blocks may beused where the surface of the bone is particularly bumpy or has tallridges and deep valleys. A thicker block may be better able to conformto the taller ridges and deeper valleys of a bone surface as compared toa thinner block. Although FIG. 18 shows a portion of the deformableblock protruding from the elongated member, this is not always the case.In other implementations, the deformable block does not protrude fromthe elongated member. For example, the deformable block may be flushwith the distal end of the elongated member. Alternatively, thedeformable block may be recessed within the distal end of the elongatedmember.

FIGS. 20-24 show various specific implementations of sensor heads havingsurfaces (or pre-formed surfaces) designed to adapt to the variousanatomical features that a bone may have. For example, the surface of abone could be flat, concave, or convex. For flat bone surfaces, thesensor head shown in FIGS. 5-6 may be desirable. This sensor head isflat or planar. An angle between the surface of the sensor head and anaxis passing through the elongated member is about 90 degrees or isperpendicular. This sensor head may be placed on bone surfaces that areflat, such as the flat, broad vertebral spinous process bone.

In contrast, for bone surfaces that are concave or convex, the sensorheads shown, for example, in FIGS. 21-24 may be more desirable than thesensor head shown in FIGS. 5-6. These sensor heads may be placed onbones that curved such as the curved aspects of the laminar plates. Thecurved surfaces of these sensor heads can make better contact (e.g.,full flat contact) with curved bone surfaces as compared to the flatsensor heads of FIGS. 5-6.

FIG. 20 shows a side view of a sensor head 2005 having a slanted orangled surface 2010. This probe can be held at an oblique angle relativeto a surface of the bone if, for example, the physician is unable tohold the probe orthogonal to the surface of the bone.

An angle 2015 is between surface 2010 and an axis 2020 which passesthrough the elongated member and the surface. The angle is less than 90degrees. For example, the angle may be about 30, 45, or 60 degrees. Theangle may range from about 30 degrees to about 89 degrees. The angle maybe less than 30 degrees or greater than 89 degrees (e.g., 89.9 degrees).

FIG. 21 shows a perspective view of a sensor head 2105 having a concavesurface 2110. The surface includes source and detector structures 2115.The surface is concave in a first or single direction 2120. The firstdirection is perpendicular (i.e., orthogonal) to an axis 2125 passingthough the elongated member and surface. This surface can complement aconvex feature or surface of the bone to be measured, such as acylindrical portion of the bone.

FIG. 22 shows a perspective view of a sensor head 2205 having a concavesurface 2210. This sensor head is similar to the sensor head shown inFIG. 21, but this sensor head is concave in two directions—a firstdirection 2215 and a second direction 2220. That is, the surface isbowl-shaped. The first direction is perpendicular to the seconddirection. The first and second directions are perpendicular to an axis2225 passing through the elongated member and surface. This surface cancomplementation a convex feature or surface of the bone to be measured,such as a ball-shaped portion of the bone.

FIG. 23 shows a perspective view of a sensor head 2305 having a convexsurface 2310. The surface includes source and detector structures 2315.The surface is convex in a first or single direction 2320. The firstdirection is perpendicular to an axis 2325 passing through the elongatedmember and surface. This surface can complement a concave feature orsurface of the bone to be measured, such as a grooved portion of thebone.

FIG. 24 shows a perspective view of a sensor head 2405 having a convexsurface 2410. This sensor head is similar to the sensor head shown inFIG. 23, but this sensor head is convex in two directions—a firstdirection 2415 and a second direction 2420. That is, the surface is domeshaped. The first direction is perpendicular to the second direction.The first and second directions are perpendicular to an axis 2425passing through the elongated member and the surface. This surface cancomplement a concave feature or surface of the bone to be measured, suchas a socket-shaped portion of the bone.

FIG. 25 shows a block diagram of a specific implementation of theinvention. A bone oximeter probe 2505 is attached to other components ofa bone oximeter system. The probe has sensors 2511-2512 that are eachconnected to an output of a multiplexer 2566. The multiplexer isconnected to an emitter 2517 which is connected to a control circuit2571 which is connected to a computer 2514. Sensors 2521-2522 areconnected to a detector 2568 which is connected to the computer via thecontrol circuit.

The computer controls operation of the bone oximeter probe. To make ameasurement using particular source and detector structures, thecomputer controls the emitter to emit radiation through sourcestructures 2511-2512. This radiation is transmitted into the bone beingevaluated and transmitted or reflected back into detector structures2321-2322. The computer, via the multiplexer, controls which sourcestructure to use to transmit the radiation. For example, the computercan control the control circuit to select the output of the multiplexercorresponding to source structure 2511. Then, radiation is transmittedthrough source structure 2511 and is not transmitted through sourcestructure 2512 because the multiplexer prevents or blocks thetransmission.

The computer receives data about the received radiation from thedetector circuit, and using information about the transmitted radiation,performs calculations to determine an oxygen saturation measurement.

Using the circuitry of FIG. 25, a user makes measurements using detectorstructures at varying distances with respect to the source structures.This information is used in making oximeter measurements at various orspecific depths in the bone. The depth of light penetration into thebone is proportional to the distance of the detector structure from thesource structure.

Although the circuitry shown is for the implementation where thecomputer via the multiplexer controls which source structures to use,one of skill in the art can make the necessary changes so that thecomputer via the multiplexer controls instead which detector structuresto use. In short, the detector and source structures are swapped and theemitter and detector are swapped. Thus, in a specific implementation,structures 2511-2512 are detector structures connected to the computervia the detector. Structures 2521-2522 are source structures connectedto the computer via the emitter. The multiplexer is connected to thecomputer through the detector.

In this specific implementation radiation is emitted through the sourcestructures. The computer via the multiplexer chooses which detectorstructure to use in making an oxygen saturation measurement. Themultiplexer can block or prevent the transmission of reflected radiationfrom a specific detector structure. The reflected radiation that themultiplexer transmits from the chosen detector structure and the spacingbetween the chosen detector structure and source structures is then usedto determine an oxygen saturation measurement.

Multiplexer 2566 is representation of a component that performs themultiplexing function. The multiplexer may be implemented usingelectrical components (such as transistors, resistors, integratedcircuits, and the like) or may be implemented mechanically (such asusing switches, gears, pulleys, and the like). The multiplexer may alsobe implemented using optical fiber, microelectromechanical systems(MEMS), mirrors, and the like. The invention may use any technique,circuit, or device that provides a multiplexing function in order toselectively receive input from (or output to) some structures connectedto the multiplexer, but not others.

Signals 2580 and 2582 can be optical signals, electrical signals, orboth. For example, if the structures include optical fiber then thesignals will be optical signals. If the structures include LEDs orphotodiodes then the signals will be electrical signals.

In an implementation signal 2580 is an optical signal and structures2511-2512 are source structures including optical fiber. In anotherimplementation signal 2580 is an electrical signal and the sourcestructures include LEDs.

In an implementation signal 2580 is an optical signal and structures2521-2522 are detector structures including optical fiber. In anotherimplementation, signal 2582 is an electrical signal and the detectorstructures include photodiodes. In a specific implementation, signal2580 is an optical signal and signal 2582 is an electrical signal. Inthis specific implementation, structures 2511-2512 include optical fiberand structures 2521-2522 include photodiodes. In another specificimplementation, signal 2580 is an electrical signal and signal 2582 isan optical signal. In this specific implementation, structures 2511-2512are source structures that include LEDs and structures 2521-2522 aredetector structures that include optical fiber. Multiplexing is furtherdiscussed in U.S. patent application Ser. No. 12/359,792, filed Jan. 26,2009, which is incorporated by reference.

FIG. 26 shows a block diagram of a specific implementation of theinvention. A bone oximeter probe 2605 has a sensor head 2610 with firstand second source structures 2615 and 2620 that are connected to firstand second beam combiners 2625 and 2626 via first and second opticalfibers 2630 and 2635. The sensor head also has detector structures2640-2641 that are connected to photodetectors 2645-2646 via opticalfibers 2650-2651. The beam combiners have inputs to receive opticalsignals from first and second light sources 2655 and 2660. Morespecifically, the first light source includes a first 690-nanometerlaser diode 2665 a and a first 830-nanometer laser diode 2665 b. Thesecond light source includes a second 690-nanometer laser diode 2670 aand a second 830-nanometer laser diode 2670 b.

The beam combiner receives various wavelengths of light from the laserdiodes and outputs the light to the source structures. The beam combinercan be used to allow a single output fiber to carry differentwavelengths of light. In brief, to make measurements using the circuitryshown in FIG. 26:

1. The first beam combiner receives a 690-nanometer wavelength of lightfrom the first light source and outputs the light onto the first opticalfiber.

2. The second beam combiner receives a 690-nanometer wavelength of lightfrom the second light source and outputs the light onto the secondoptical fiber.

3. The first beam combiner receives an 830-nanometer wavelength of lightfrom the first light source and outputs the light onto the first opticalfiber.

4. The second beam combiner receives an 830-nanometer wavelength oflight from the second light source and outputs the light onto the secondoptical fiber.

A more detailed discussion of the operation is as follows: In a firststep, the first light source (or 690-nanometer laser diode of the firstlight source) produces a 690-nanometer wavelength of light that istransmitted to the first beam combiner. The first beam combiner outputsthe 690-nanometer light onto the first optical fiber, through the firstsource structure, and into the bone. The photodetectors detect thereflected 690-nanometer light from the bone. During the first step, theother laser diodes (i.e., diodes 2665 b and 2670 a-b) remain off.Alternatively, the first beam combiner, second beam combiner, or bothcan block light from the other laser diodes so that the light is nottransmitted through the source structures. A multiplexer or multiplexingoperation, as shown in FIG. 25 and discussed above, may be used to blockthe light.

In a second step, the second light source (or 690-nanometer laser diodeof the second light source) produces a 690-nanometer wavelength of lightthat is transmitted to the second beam combiner. The second beamcombiner outputs the 690-nanometer light onto the second optical fiber,through the second source structure, and into the bone. Thephotodetectors detect the reflected 690-nanometer light from the bone.During the second step, similar to the first step, the other laserdiodes (i.e., diodes 2665 a-b and 2670 b) remain off or the beamcombiners block the light from the other laser diodes.

In a third step, the first light source (or 830-nanometer laser diode ofthe first light source) produces an 830-nanometer wavelength of lightthat is transmitted to the first beam combiner. The first beam combineroutputs the 830-nanometer light onto the first optical fiber, throughthe first source structure, and into the bone. The photodetectors detectthe reflected 830-nanometer light from the bone. During the third step,similar to the first step, the other laser diodes (i.e., diodes 2665 aand 2670 a-b) remain off or the beam combiners block the light from theother laser diodes.

In a fourth step, the second light source (or 830-nanometer laser diodeof the second light source) produces an 830-nanometer wavelength oflight that is transmitted to the second beam combiner. The second beamcombiner outputs the 830-nanometer light onto the second optical fiber,through the second source structure, and into the bone. Thephotodetectors detect the reflected 830-nanometer light from the bone.During the fourth step, similar to the first step, the other laserdiodes (i.e., diodes 2665 a-b and 2670 a) remain off or the beam combineblock the light from the other laser diodes.

It should be appreciated that these steps can occur in any order. Forexample, the first and second steps may be swapped. The 830-nanometerwavelength of light may be transmitted into the bone before the690-nanometer wavelength of light is transmitted into the bone.

Thus, with the beam combiner, a single output fiber (e.g., first opticalfiber 2630), can be used to output via a source structure (e.g., firstsource structure 2615) light of a first wavelength (e.g., 690nanometers) and light of a second wavelength (e.g., 830 nanometers),different from the first wavelength. That is, at a first time, thesource structure outputs light of the first wavelength. At a secondtime, different from the first time, the source structure outputs lightof the second wavelength.

The use of a beam combiner allows for a small and compact sensor head(i.e., small sensor head surface area) because it allows a single fiberto output different wavelengths of light, thus removing the need to havemultiple output fibers at the sensor head, each dedicated to outputtinga specific wavelength of light. Small sensor heads can be more desirablethan large sensor heads because the small sensor heads can be advancedthrough small incisions to the underlying bone. Small incisions aregenerally more desirable than large incisions because with smallincisions there is less blood loss for the patient. There can also beshorter recuperation times, less pain, and less scaring with smallincision as compared to large incisions.

In a specific implementation, the first beam combiner, second beamcombiner, or both are external to the probe and are inside a system unitor console of the bone oximeter system such as console 303 shown in FIG.3. That is, the beam combiners and light sources are all contained in asingle container, i.e., console 303. In another implementation, thefirst beam combiner, second beam combiner, or both are external to theprobe and to the console. In this specific implementation, the beamcombiners are connected between the console and the probe. For example,the beam combiners may have an input port that is connected to theconsole and an output port that is connected to the probe. The inputport allows the beam combiner to receive optical signals from theconsole. The output port allows the beam combiner to output the receivedlight to the probe.

Some embodiments will not have a beam combiner. For example, instead ofa single shared fiber, an optical fiber may connect a source structureto a laser diode directly instead of connecting the source structure toa beam combiner. Not having a beam combiner can reduce the cost of theoximeter system. Although FIG. 26 shows two beam combiners, anembodiment may have a single beam combiner to, for example, reduce cost.In this specific embodiment, the second beam combiner shown in FIG. 26is eliminated. Second optical fiber 2635 is connected to the690-nanometer laser diode of the second light source. The probe mayinclude a third source structure to hold an end of a third optical fiberwhich connects to the 830-nanometer laser diode of the second lightsource.

Thus, it should be appreciated that a bone oximeter system can have anynumber of beam combiners including zero or no beam combiners dependingon factors such as desired cost and desired sensor head size. Forexample, if a higher priority is given to cost as compared to sensorhead size, an implementation may include no beam combiners to lower thecost of the system. Conversely, if a higher priority is given to asensor head size as compared to cost, an implementation may include beamcombiners to help reduce the size of the sensor head.

In the example shown in FIG. 26, the beam combiners each have two inputsand one output (i.e., 2-to-1). But, a beam combiner can have any numberof inputs and any number of outputs (e.g., four inputs and two outputsor 4-to-1). However, the cost of a beam combiner generally increaseswith an increasing number of inputs and outputs. Thus, in some cases itwill be more economical to select two 2-to-1 beam combiners as comparedto selecting a single 4-to-1 beam combiner. In other cases, a single4-to-1 beam combiner may be selected over two 2-to-1 beam combiners if,for example, the 4-to-1 beam combiner is smaller than two 2-to-1 beamcombiners and a small console size is a high priority.

FIG. 27 shows a flowchart for making an oxygen saturation measurementfor a bone. In a step 2705, a bone oximeter probe is inserted into abody through an incision. The tip of the probe is directed towards atarget bone. In a specific implementation, the probe is inserted by asurgeon who holds the probe. In another specific implementation, theprobe is inserted into the body by a robot or a robotic arm. The probecan be visualized inside the body using X-ray, ultrasound, or othervisual aid techniques. The tip of the probe may include a camera andlights for the camera so that probe's advancement into the incision canbe seen on a video monitor. Alternatively or additionally, when the tipof the probe reaches its target location (e.g., target bone), thesurgeon can feel or the robot can detect the resistance in the probewhen the sensor head contacts or hits the target bone.

In a step 2710, the doctor positions the probe so that the probe sensorhead contacts or is near the target bone to be measured. For example,the doctor may angle or adjust the probe within the incision so that thesurface of the sensor head makes good contact with the surface of thetarget bone.

In a step 2715, the doctor causes the measurement of one or more ofparameters associated with the target bone. Some examples of measurementinclude returned signal level, oxygen saturation, hemoglobinconcentration, blood flow, and pulse.

In a specific implementation, the doctor activates the bone oximeterconsole (e.g., turns on console) so that a first light signal istransmitted in a first direction from the console, through the boneoximeter probe (e.g., through a first fiber optic cable of the probe),and into the target bone. The doctor maintains a position of the probeat the bone so that the probe can receive a reflection of the firstlight signal from the bone (i.e., a second light signal). The secondlight signal is transmitted via a second fiber optic cable in a seconddirection, opposite the first direction, to the console. A calculationis made at the console based on the first and second light signals. Thecalculation or a value or bone measurement based on the calculation maybe displayed on an electronic display of the console for the doctor toread.

In other words, light is transmitted through optical fibers of the boneoximeter probe through openings in the sensor unit located at the tip ofthe probe. Light scatters in a bone located at or nearby the tip of theprobe, and reflected light is detected by the sensor unit, which isreturned to a monitoring console. Based on the initial light and thereflected light information, the console can measure and calculatevarious parameters associated with the bone. These parameters include asignal level of returned light, an oxygen saturation level, a totalhemoglobin concentration, a blood flow, and a pulse.

In a step 2720, the doctor selects a course of action based on one ormore of the measured parameters. The specific course of action may varywidely depending on, for example, what specific parameter was measured,the patient's condition, health, or age, and so forth. For example,immature skeletons (e.g., persons less than 19 years old) may be moreoxygenated than mature skeletons (e.g., persons older than 65 yearsold).

In a specific implementation, the parameter is a signal qualitymeasurement. The doctor can determine whether the signal quality issufficient (i.e., there is good contact between the sensor head and thebone) or whether the signal quality is insufficient. If the signalquality is sufficient the doctor may decide to continue monitoring atthat specific location on the bone. If the signal quality isinsufficient the doctor may reposition the probe at a different locationon the bone and make another signal quality measurement to determinewhether that different location is suitable to make an oxygen saturationmeasurement of the bone.

In another specific implementation, the parameter provides an indicationof the health of the bone. The measured parameter may be a tissueoxygenation value of the bone, a hemoglobin concentration value of thebone, or both. These values or bone measurements can be used in bonesurgery to determine whether one course of action is more appropriate ordesirable than another course of action. For example, bone fractures orbreaks may be repaired using pins, nails, screws, plates, bioresorbablematerials, anchors, and other types of hardware. The bone oximeterprovides the surgeon with objective measurements on the health of thebone and can help the surgeon decide which type of hardware, surgicalprocedure, or both is appropriate for the patient.

Surgeons performing spine bone surgery, such as spine fusion surgery,may use the information provided by the bone oximeter to help themdecide upon a method of fusion. The rates of spine fusion surgery havebeen increasing rapidly over the last 20 years with almost a fourfoldincrease in rates between 1992 and 2003 (0.3 per 100,000 to 1.1 per100,000). There were about 575,000 spinal surgery discharges in theUnited States in 2005 with about 331,000 of these involving fusions. Anon-solid fusion or pseudarthrosis is associated with a poor outcome forthe patient and can lead to further expense in the future with revisionsurgeries.

One method of promoting fusion is to place bone graft in the fusion siteand the incorporation of this is an interaction between graft and hostcharacteristics. Autogenous bone grafts make use of the specialimmunogenic status and better vascularity of donor site bone stock andcan be well incorporated by the spine. They are generally taken from theiliac crest and as well as being limited in quantity, graft site relatedmorbidity has been estimated at up to 20 percent for autogenous grafts,and so there is also a need for allografts and bone substitutes. One ofthe most studied and frequently used biologic alternatives to auto graftis bone morphogenetic protein (BMP). The application kit for therhBMP-2ACS costs about $5000 and is generally paid by the hospital.

Currently, the decision about which of these grafts to use is based onthe surgeon's opinion of the risk factors for bone quality. This boneoximeter can provide an objective measurement of the quality of bone byits StO2 and can make selection of bone graft more consistent andquantifiable. With these measurements, the surgeon is better informed asto whether it is necessary to use the expensive BMP graft or whetherthere is sufficient vascularity in the bone for standard (and cheaper)grafts such as cadaveric allograft ($800). A bone that is welloxygenated may incorporate a standard bone graft such as an allograftwhich is less expensive than a BMP graft.

Assessment of bone quality would also help to ensure that correct graftsare chosen for each patient, increasing the likelihood of a solid fusionand so reducing the frequency of pseudarthrosis. A further saving ofmeasuring bone quality is that the cost of fusion and then revisionfollowing pseuadarthrosis is around $127,000 compared to $75,000 forsurgery using BMP and a much lower probability of revision. The correctselection of grafts can save money both in cases of over use ofexpensive options and also in the consequences of their underuse.

As further background, the biological sequence of bone graftincorporation starts with haematoma formation and release of growthfactors. Inflammation occurs and there is a migration and proliferationof mesenchymal cells around the graft site. Vessels invade the graftfollowed by focal osteoclastic resorption of donor bone. Finallyintramembranous, endochondral bone formation, or both occurs on thegraft surfaces and remodeling begins to provide structural support.

The decision about which graft will be used is typically based on thesurgeon's opinion and their consideration of risk factors for bonevascularisation, as without good vascularity bone graft incorporation isslow and there is an increased chance of pseudarthrosis. The factorsinfluencing the surgeon's decision include age, with pseudarthrosisrates of around 2-3 percent reported in children as opposed to up to 43percent in adults. Smoking is also a strong predictor with heavy smokingand nicotine reducing bone vascularization. Any local neoplastic processwill lead to abnormal new bone formation at the site including bothbenign and malignant growths. Intense irradiation of an area will reducevascularization through scarring in a similar way to sclerotic bone fromprevious fusions. Osteopenic bone may mechanically be unable to supportsupplemental material if it must bear load. Systemicallyanti-inflammatory agents and glucocorticoids will also have the effectof suppressing bone remodeling.

Other factors that can affect bone oxygenation include medications(e.g., non-steroidal anit-inflamatory drugs or NSAIDs), steroids,osteopenia (e.g., bone densitometry record or DEXA record),cardiovascular disease, chronic obstructive pulmonary disease (e.g.,COPD), asthma, diabetes, radiation, previous spinal fusions, orcombinations of these.

Measurements for the bone can be performed at or near the time ofsurgery. The bone oximeter can detect and continuously monitory hypoxicchanges in bone. Tissue oxygenation differences between normal andhypoxic bone may be about 15-20 percentage points in the presence of astable hemoglobin concentration. This difference may be seen after about20 minutes.

It should be understood that the specific flow example shown in FIG. 27is not limited to the specific flows and steps shown. A flow of theinvention may have additional steps (not necessarily described in thisapplication), different steps which replace some of the steps presented,fewer steps or a subset of the steps presented, or steps in a differentorder than presented, or any combination of these. Further, the steps inother implementations of the invention may not be exactly the same asthe steps presented and may be modified or altered as appropriate for aparticular application or based on the data or situation.

For example, before step 2705, the doctor or a nurse may clean thesurface of the target bone to be measured so that any fluids, such asblood, do not interfere with the measurements. However, there can besome fluids such as thin blood layer between the bone surface and thesensor because the layer will be very thin in comparison to with thebone thickness.

FIG. 28 shows one implementation of the invention where a bone oximeterprobe is used during a surgical repair of a broken leg bone. The figureshows a side view of a patient's lower leg 2810 in which there is afracture 2812 of a tibia bone 2815. A bone oximeter probe 2820 isinserted through an incision in soft tissue 2825. The probe is advancedthrough the soft tissue until a sensor head 2830 of the probe reaches orcontacts a target bone (i.e., the tibia bone). Once the sensor headreaches or contacts a surface of the target bone, measurements of thebone can be made.

In a specific implementation, the system transmits optical signals intothe target bone and receives reflected signals from the bone todetermine, for example, a tissue oxygenation level, a hemoglobinconcentration, or both. Other examples of bone measurements that may bemade include information indicating blood vessel density of a region ofthe bone which is roughly proportional to the hemoglobin concentration.

These measurements can indicate to the doctor the health or viability ofthe bone and can help the surgeon determine or select a specific courseof action. For example, in addition to screws and plates to repair thebroken bone, additional reinforcement may also be used if oxygenationmeasurements of the bone indicate that the bone is unhealthy.

The system and methods for bone oximetry discussed in this applicationcan be applied to any bone for which measurements are desired.Generally, any bone in the body (e.g., human or animal body) could bemeasured so long as the bone has a sufficient surface area for thesensor head and is accessible (e.g., accessible in surgery). Forexample, for spinal surgery, bone measurements can be made for the spinebone (e.g., lumbar vertebra). The sensor head can be placed on any partof the spine bone such as the spinous process, lamina, articular facet,transverse process (e.g., right and left transverse process), vertebralcanal, or pedical. Bone measurements can be made for any type of bone,such as long bones, short bones, flat bones, irregular bones, sesamoidbones, cranial bones, the skull, the mandible, and facial bones. Thebones may be located in the middle ear, throat, shoulder girdle, thorax,vertebral column, arms, hands, pelvis, thighs, legs, and feet.

Bones located in the shoulder girdle include the scapula or shoulderblade and the clavicle or collarbone. Bones located in the vertebralcolumn include the cervical vertebrae, thoracic vertebrae, and lumbarvertebrae. Bones located in the arms and forearms include the humerus,radius, and ulna. Bones located in the hands include carpal or wristbones (e.g., scaphoid, lunate, triquetral, pisiform, trapezium,trapezoid, capitate, and hamate bone), metacarpus or palm bones, anddigits of the hands (e.g., proximal, intermediate, and distalphalanges). Bones located in the pelvis include the coccyx, sacrum, andhip bone. Bones located in the thighs and legs include the femur,patella, tibia, and fibula or fibular. Bones located in the feet includethe tarsal or ankle bones (e.g., calcaneus, talus, navicular, medialcuneiform, intermediate cuneiform, lateral cuniform, and cuboid bone),and metatarsus bones. To measure bone oxygenation, the sensor head maybe placed on spongy bone (long bone horizontal section), medullarycavity marrow, muscle, adipose over periosteum, periostium, tendon,articular cartilage, meniscus, epiphysis, and periostium with littlemuscle or no muscle. Furthermore, the bone oximeter probe and techniquesfor bone oximetry discussed in this application may be applied tononhuman patients such as pigs (e.g., porcine bone measurements), dogs,cats, birds, horses, monkeys, rabbits, rats, apes, cows, and so forth.Specifically, the bone oximeter probe may be used to measure oxygensaturation of bovine long bone and the spinous process or skull of apig.

A specific example of a surgical procedure in which the bone oximetermay be used includes an osteotomy such as an osteotomy of the hip, knee,or jaw. An osteotomy is a surgical operation where a bone is cut toshorten, lengthen, or change its alignment. It is sometimes performed tocorrect a hallux valgus, or to straighten a bone that has healedcrookedly following a fracture. It is also used to correct a coxa vara,genu valgum, and genu varum. Osteotomy may be used to relieve pain inarthritis, especially of the hip and knee.

The bone oximeter probe may be used with tools for lateral lumbarsurgery. Some of these tools are discussed in U.S. patent applicationSer. Nos. 12/568,420, and 12/568,470 filed Sep. 28, 2009 which areincorporated by reference.

Another application for bone oximetry includes bone cancer or bonecancer treatments such as detecting bone cancer, treating bone cancer,and surgical procedures to remove bone cancer. Thus, in addition tousing bone oximeter measurements in decision making as to whether or notto use specific bone graft additives such as bone morphogentic protein(BMP) to improve bone fusion outcomes, the sensor may also be used inassessing the viability of bone anywhere in the body. For example, inhead and neck cancer surgery, tumors that occur in the jaw bone (oralcancers) may be radiated and then resected. However, all nonviable bone(often caused by radiation treatment damage, known asradioosteonecrosis) is typically removed along with the tumor.Information on what regions of the bone are nonviable can lead toreduced postoperative complications.

This application describes aspects of the invention in connection with ahandheld bone oximeter tool or probe. However, the principles of theinvention are also applicable to a bone oximeter tool or other tool witha bone oximeter sensor when implemented in an endoscopic instrument.Endoscopy is a minimally invasive diagnostic medical procedure that isused to assess the interior surfaces of an organ by inserting a tubeinto the body. At the end of the endoscope tool is a bone oximetersensor or tool as described in this application.

The endoscopic instrument with a bone oximeter or other tool with a boneoximeter sensor at the end can have a robotic interface. The roboticinterface allows a doctor control the instrument from a remote location.For example, the doctor in New York City can use a tool of the inventionto perform a remote procedure on a patient who is located in Barrows,Ak. The doctor will be able to make oxygen saturation measurement of thepatient's bone using the bone oximeter probe or other tool. The roboticinterface may have a haptic interface which provides feedback to thedoctor, or may not have a haptic interface. When a haptic interface forthe tool is not available, the readings provided by the tool may givethe doctor an indication of the condition of a bone.

A specific flow example for making a bone oximeter probe is presentedbelow, but it should be understood that the invention is not limited tothe specific flows and steps presented. A flow of the invention may haveadditional steps (not necessarily described in this application),different steps which replace some of the steps presented, fewer stepsor a subset of the steps presented, or steps in a different order thanpresented, or any combination of these. Further, the steps in otherimplementations of the invention may not be exactly the same as thesteps presented and may be modified or altered as appropriate for aparticular application or situation.

In a specific implementation, a method includes:

1. Creating a set of channels, holes, or openings through a block. Thechannels are created such that they extend through the block, i.e., froma front surface of the block to a back surface of the block, oppositethe front surface. Any technique may be used to create the channels. Forexample, the channels may be created by drilling, milling, boring,plunging, punching, laser cutting, or combinations of these.

2. Threading a fiber optic cable into each channel. That is, an end ofthe fiber optic cable is inserted into the channel. In a specificimplementation, the end of the fiber optic cable is inserted through theback surface of the block and is advanced through the channel towardsthe front surface of the block. The fiber optic cable may be positionedwithin the channel such that the end is flush with the front surface,the end protrudes out from the front surface, or the end is recessedbelow the front surface. In another specific implementation, an oppositeend of the fiber optic cable is inserted through front surface of theblock, is advanced through the channel towards the back surface of theblock, and exits the back surface.

3. Attaching the fiber optic cable to the channel. An adhesive such asepoxy may be used to attach the fiber optic cable to the channel. Theepoxy may be applied at the back surface of the block, front surface ofthe block, or both and then allowed to flow into the channel.

4. Attaching the block to a distal end of a rigid elongated member.Epoxy may be used to attach the block to the elongated member. In aspecific implementation, the fiber optic cable is threaded through theelongated member before the attaching the fiber optic cable to thechannel in the block. That is, during the attaching the fiber opticcable to the channel, a portion of the fiber optic cable is lying in apassageway of the elongated member. In another implementation, the fiberoptic cable is threaded through the elongated member after the attachingthe fiber optic cable to the channel in the block.

In a specific implementation, a method for making a bone oximeter probeincludes providing a sensor head cylinder and tube. Creating one or moreholes in the sensor head cylinder. Attaching fiber optic cable to eachof the one or more holes of the sensor head cylinder. Applying anadhesive such as epoxy to at least one of the sensor head cylinder ortube. Inserting the sensor head cylinder into the tube. In this specificimplementation, a diameter of the sensor head cylinder is slightly lessthan an inner diameter of the tube. This simplifies manufacturing byallowing the sensor head cylinder to be inserted into the tube andproviding a space for the adhesive to flow.

In a specific implementation, a method for making a bone oximeter probehaving a pad to conform to a surface of a bone to be measured includes:

1. Attaching the pad to a block using, for example, an adhesive to jointhe pad and block together.

2. Creating a set of channels through the pad and block. The channelsare created so that each channel extends from a front or bone facing orbone contacting surface of the pad to a back surface of the block,opposite the front surface. In a specific implementation, the channelsare created after the pad and block are attached. In anotherimplementation, the channels are created before the pad and block areattached. In this specific implementation, a first set of channels orholes are created in the pad. A second set of channels are created inthe block. The first and second set of channels are then aligned andafterwards, the pad is attached to the block.

3. Threading a fiber optic cable into each channel.

4. Positioning the fiber optic cable within each channel so that an endof the fiber optic cable is flush with the front surface of the pad. Inanother implementation, the end of the optic cable is positioned so thatit is below the front surface of the pad and between the front surfaceof the pad and the back surface of the block. That is, the end of thecable is recessed below the front surface of the pad so that there is agap within the channel between the end of the cable and the frontsurface of the pad. In other words, a thickness of the block and pad inthe uncompressed state (or a distance from the back surface of the blockto the front surface of the pad) is greater than a distance from theback surface of the block to the end of the fiber optic cable. When thepad is compressed by being deformed around the surface of the bone, theend of the cable will be brought in close proximity to the surface ofthe bone.

5. Attaching the fiber optic cable to the channel.

6. Attaching the block to a distal end of a rigid elongated member(e.g., tube) such that at least a portion of the pad extends out fromthe distal end so that the pad can be compressed. In other words, adistance from a proximal end of the elongated member to the distal endis less than a distance from the proximal end to the front surface ofthe pad.

In a specific implementation, the attaching the block to the elongatedmember includes threading the fiber optic cable through a passageway inthe elongated member after the attaching the fiber optic cable to thechannel. In this specific implementation, the block and pad or end ofthe cable may be inserted into a proximal end of the elongated memberand advanced towards the distal end. Alternatively, an opposite end ofthe cable may be inserted into the distal end of the elongated memberand advanced towards the proximal end where it then exits the proximalend.

In another implementation, the attaching the block to the elongatedmember includes threading the fiber optic cable through a passageway inthe elongated member before the attaching the fiber optic cable to thechannel.

This description of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form described, and manymodifications and variations are possible in light of the teachingabove. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications.This description will enable others skilled in the art to best utilizeand practice the invention in various embodiments and with variousmodifications as are suited to a particular use. The scope of theinvention is defined by the following claims.

The invention claimed is:
 1. A method of making an oxygen saturationmeasurement for a bone comprising: advancing an elongated probe throughan incision in a tissue, wherein the probe comprises: a first tube; asensor head, coupled to the first tube; and first and second fiber opticcables, coupled to the sensor head, wherein ends of the first and secondfiber optic cables are exposed on a surface of the sensor head, and anaxis passing through the first tube passes through the surface;positioning the elongated probe in the tissue so the sensor headcontacts a bone for which an oxygen saturation parameter is to bemeasured; causing transmitting of a first light signal through the firstfiber optic cable to the sensor head, wherein from the sensor head, thefirst light signal is directed at the bone; after causing transmittingof the first light signal through the first fiber optic cable,maintaining a position of the probe at the bone for the probe to receivea reflection of the first light signal from the bone, wherein thereflection of the first light signal from the bone is a second lightsignal; and causing transmitting of the second light signal via thesecond fiber optic cable, wherein the second light signal is transmittedin a direction opposite of the transmitting of the first light signal.2. The method of claim 1 wherein the sensor head comprises: a firstsource opening, wherein the first fiber optic cable is coupled to thefirst source opening; and a first detector opening, wherein the secondfiber optic cable is coupled to the first detector opening, and adistance between the first source opening and the first detector openingis about 3.5 millimeters or less.
 3. The method of claim 1 wherein thesurface of the sensor head has a surface area of about 24 squaremillimeters or less.
 4. The method of claim 1 wherein the probe furthercomprises: a second tube, extending from a proximal end of the firsttube to a connector for coupling the probe to a console, wherein thesecond tube comprises a flexible material and the first tube comprises arigid material.
 5. The method of claim 1 comprising: coupling aconnector of the probe to a console comprising an electronic display;after causing transmitting of the first light signal through the firstfiber optic cable and causing transmitting of the second light signalvia the second fiber optic cable, causing a calculation in the consoleof an oxygen saturation parameter associated with the first light signaland second light signal; and causing displaying of the oxygen saturationparameter on the electronic display.
 6. The method of claim 5 whereinthe oxygen saturation parameter comprises at least one of an oxygensaturation level value of the bone or a total hemoglobin concentrationvalue of the bone that was measured.
 7. The method of claim 1 whereinthe fiber optic cables extend through a passageway within the probe tothe sensor head.
 8. The method of claim 1 wherein the sensor headcomprises: a first source structure; a second source structure; a firstdetector structure, wherein the first detector structure comprises thesecond fiber optic cable; and a second detector structure, wherein afirst distance extends between the first source structure and the firstdetector structure without touching another source or detectorstructure, a second distance extends between the second source structureand the second detector structure without touching another source ordetector structure, and the first distance is different from the seconddistance.
 9. The method of claim 1 wherein the sensor head comprises: afirst source structure comprising the first fiber optic cable; a secondsource structure; a first detector structure comprising the second fiberoptic cable; and a second detector structure, wherein the first sourcestructure, second source structure, first detector structure, and seconddetector structure are arranged on a line and the axis is perpendicularto the line.
 10. The method of claim 1 wherein the sensor headcomprises: a first source structure comprising the first fiber opticcable; and a first detector structure comprising the second fiber opticcable, wherein distances between the first source structure and an edgeof the surface and between the first detector structure and the edge areabout 1.5 millimeters or less.
 11. The method of claim 1 wherein thepositioning the elongated probe in the tissue comprises positioning theelongated probe in the tissue so the sensor head contacts a firstlocation on the bone, and the method further comprises: after thecausing transmitting of the second light signal, reading a first signalquality value on an electronic display of a console; repositioning theelongated probe in the tissue so the sensor head contacts a secondlocation on the bone, different from the first location; and after therepositioning the elongated probe, reading a second signal quality valueon the electronic display of the console.
 12. The method of claim 1wherein the sensor head comprises a deformable block, wherein a surfaceof the sensor head can deform to adapt to a surface contour of the boneto be measured, and the first and second optic cables that pass throughthe deformable block to the surface of the sensor head can slide withina passageway of the first tube as the deformable block is beingdeformed.
 13. The method of claim 1 wherein the sensor head comprises atleast a first, second, and third sensor opening, the first fiber opticcable is coupled to the first sensor opening, and the second fiber opticcable is coupled to the second sensor opening, and the first, second,and third openings are arranged in a line.
 14. The method of claim 1wherein the sensor head comprises at least a first, second, and thirdsensor opening, the first fiber optic cable is coupled to the firstsensor opening, and the second fiber optic cable is coupled to thesecond sensor opening, and the first and second openings are arranged ina first line, and the second and third openings are arranged in a secondline that is not in-line with the first line.
 15. The method of claim 1wherein the sensor head comprises at least a first, second, third, andfourth sensor opening, the first fiber optic cable is coupled to thefirst sensor opening, and the second fiber optic cable is coupled to thesecond sensor opening, and the first, second, and third openings arearranged in a line, and the fourth sensor opening is not in-line withthe first, second, and third openings.
 16. The method of claim 1 whereinthe sensor head comprises at least a first, second, third, and fourthsensor opening, the first fiber optic cable is coupled to the firstsensor opening, and the second fiber optic cable is coupled to thesecond sensor opening, and the first and second openings are separatedby a first distance, the third and fourth openings are separated by asecond distance, the second and third openings are separated by a thirddistance, and the third distance is greater than the first distance andthe second distance.
 17. The method of claim 1 wherein the sensor headcomprises a first, second, third, and fourth sensor opening, the firstfiber optic cable is coupled to the first sensor opening, and the secondfiber optic cable is coupled to the second sensor opening, and thefirst, second, third, and fourth openings form corners of aquadrilateral shape, the first and second openings are separated by afirst distance, the second and third openings are separated by a seconddistance, and the first distance is different from the second distance.18. The method of claim 17 wherein the second and fourth openings areseparated by a third distance, and the third distance is different fromthe first distance and second distance.
 19. The method of claim 1wherein the sensor head comprises four or fewer sensor openings on thesurface, the sensor openings comprise a first and second sensor opening,the first fiber optic cable is coupled to the first sensor opening, andthe second fiber optic cable is coupled to the second sensor opening.20. The method of claim 1 wherein the sensor head comprises three orfewer sensor opening on the surface, the sensor openings comprise afirst and second sensor opening, the first fiber optic cable is coupledto the first sensor opening, and the second fiber optic cable is coupledto the second sensor opening.
 21. The method of claim 1 wherein thesensor head comprises at most two sensor openings on the surface, thesensor openings comprise a first and second sensor opening, the firstfiber optic cable is coupled to the first sensor opening, and the secondfiber optic cable is coupled to the second sensor opening.
 22. Themethod of claim 1 wherein the surface of the sensor head is a firstsurface of the sensor head, the sensor head further comprises third andfourth fiber optic cables coupled to a second surface of the sensorhead, and the second surface is not planar with the first surface. 23.The method of claim 1 wherein the surface of the sensor head isperpendicular to the axis passing through the first tube and thesurface.
 24. The method of claim 1 wherein the surface of the sensorhead is not perpendicular to the axis passing through the first tube andthe surface.